U.S. patent application number 16/397737 was filed with the patent office on 2019-08-15 for method and user equipment for receiving dowlink channel, and method and base station for transmitting downlink channel.
This patent application is currently assigned to LG ELECTRONICS INC.. The applicant listed for this patent is LG ELECTRONICS INC.. Invention is credited to Kijun KIM, Yunjung YI, Hyangsun YOU.
Application Number | 20190253291 16/397737 |
Document ID | / |
Family ID | 59020936 |
Filed Date | 2019-08-15 |
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United States Patent
Application |
20190253291 |
Kind Code |
A1 |
YOU; Hyangsun ; et
al. |
August 15, 2019 |
METHOD AND USER EQUIPMENT FOR RECEIVING DOWLINK CHANNEL, AND METHOD
AND BASE STATION FOR TRANSMITTING DOWNLINK CHANNEL
Abstract
A method and apparatus for transmitting/receiving a downlink
channel in a wireless communication system are provided. A downlink
control channel and a downlink data channel corresponding to the
downlink control channel are transmitted/received within a
transmission time interval (TTI). A reference signal (RS) of an
antenna port used for transmission of both the downlink control
channel and the downlink data channel is transmitted/received on an
OFDM symbol with the downlink control channel, and an RS of an
antenna port used only for transmission of the downlink data
channel is transmitted in the remaining OFDM symbol(s) of the
TTI.
Inventors: |
YOU; Hyangsun; (Seoul,
KR) ; KIM; Kijun; (Seoul, KR) ; YI;
Yunjung; (Seoul, KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
LG ELECTRONICS INC. |
Seoul |
|
KR |
|
|
Assignee: |
LG ELECTRONICS INC.
Seoul
KR
|
Family ID: |
59020936 |
Appl. No.: |
16/397737 |
Filed: |
April 29, 2019 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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15374737 |
Dec 9, 2016 |
10313168 |
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16397737 |
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62266000 |
Dec 11, 2015 |
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62335653 |
May 12, 2016 |
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62335703 |
May 13, 2016 |
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62401935 |
Sep 30, 2016 |
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62405216 |
Oct 6, 2016 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04L 5/0082 20130101;
H04L 5/0048 20130101; H04L 5/001 20130101; H04L 5/0023 20130101;
H04L 27/2602 20130101; H04L 5/0035 20130101 |
International
Class: |
H04L 27/26 20060101
H04L027/26; H04L 5/00 20060101 H04L005/00 |
Claims
1. A method of receiving a downlink channel by a user equipment,
the method comprising: receiving first transmission mode (TM)
configuration information; and receiving a first physical downlink
channel based on the first TM configuration information, wherein
the first physical downlink channel has a short transmission
interval (TTI) duration equal to or short than a duration of a slot
in a time domain, wherein the first TM configuration information
includes information regarding a first TM for the short TTI
duration and information regarding a second TM for the short TTI
duration, wherein the first physical downlink channel is received
based on the first TM when the first physical downlink channel is
received in a multimedia broadcast multicast service (MBSFN)
subframe, and wherein the first physical downlink channel is
received based on the second TM when the first physical downlink
channel is received in a non-MBSFN subframe.
2. The method according to claim 1, wherein the first TM is one
among a plurality of TMs which use a demodulation reference signal
(DMRS), and wherein the second TM is one among a plurality of TMs
which use the DMRS or cell-specific reference signal (CRS).
3. The method according to claim 1, further comprising: receiving a
second physical downlink channel based on second TM configuration
information, wherein the second physical downlink channel has a
non-short TTI duration longer than the duration of the slot in the
time domain, wherein the second TM configuration information
includes information regarding one TM for the non-short TTI
duration, wherein the second physical downlink channel is received
based on the one TM irrespective of whether the second physical
downlink channel is received in the MBSFN subframe or in the
non-MBSFN subframe.
4. The method according to claim 1, wherein the duration of the
slot is 0.5 ms in the time domain.
5. A user equipment for receiving a downlink channel, comprising: a
transceiver; and a processor configured to control the transceiver,
the processor configured to: control the transceiver to receive
first transmission mode (TM) configuration information; and control
the transceiver to receive a first physical downlink channel based
on the first TM configuration information, wherein the first
physical downlink channel has a short transmission interval (TTI)
duration equal to or short than a duration of a slot in a time
domain, wherein the first TM configuration information includes
information regarding a first TM for the short TTI duration and
information regarding the second TM for the short TTI duration,
wherein the first physical downlink channel is received based on
the first TM when the first physical downlink channel is received
in a multimedia broadcast multicast service (MBSFN) subframe, and
wherein the first physical downlink channel is received based on
the second TM when the first physical downlink channel is received
in a non-MBSFN subframe.
6. The user equipment according to claim 5, wherein the first TM is
one among a plurality of TMs which use a demodulation reference
signal (DMRS), and wherein the second TM is one among a plurality
of TMs which use the DMRS or cell-specific reference signal
(CRS).
7. The user equipment according to claim 5, wherein the processor
is configured to control the transceiver to receive a second
physical downlink channel based on second TM configuration
information, wherein the second physical downlink channel has a
non-short TTI duration longer than the duration of the slot in the
time domain, wherein the second TM configuration information
includes information regarding one TM for the non-short TTI
duration, wherein the second physical downlink channel is received
based on the one TM irrespective of whether the second physical
downlink channel is received in the MBSFN subframe or in the
non-MBSFN subframe.
8. The user equipment according to claim 5, wherein the duration of
the slot is 0.5 ms in the time domain.
9. An apparatus, comprising: a processor; and a memory that is
operably connectable to the processor and that has stored thereon
instructions which, when executed, cause the processor to perform
operations comprising: controlling a transceiver to receive first
transmission mode (TM) configuration information; and controlling
the transceiver to receive a first physical downlink channel based
on the first TM configuration information, wherein the first
physical downlink channel has a short transmission interval (TTI)
duration equal to or short than a duration of a slot in a time
domain, wherein the first TM configuration information includes
information regarding a first TM for the short TTI duration and
information regarding the second TM for the short TTI duration,
wherein the first physical downlink channel is received based on
the first TM when the first physical downlink channel is received
in a multimedia broadcast multicast service (MBSFN) subframe, and
wherein the first physical downlink channel is received based on
the second TM when the first physical downlink channel is received
in a non-MBSFN subframe.
10. The apparatus according to claim 9, wherein the first TM is one
among a plurality of TMs which use a demodulation reference signal
(DMRS), and wherein the second TM is one among a plurality of TMs
which use the DMRS or cell-specific reference signal (CRS).
11. The apparatus according to claim 9, wherein the operations
further comprises: controlling the transceiver to receive a second
physical downlink channel based on second TM configuration
information, wherein the second physical downlink channel has a
non-short TTI duration longer than the duration of the slot in the
time domain, wherein the second TM configuration information
includes information regarding one TM for the non-short TTI
duration, wherein the second physical downlink channel is received
based on the one TM irrespective of whether the second physical
downlink channel is received in the MBSFN subframe or in the
non-MBSFN subframe.
12. The apparatus according to claim 9, wherein the duration of the
slot is 0.5 ms in the time domain.
13. A method of transmitting a downlink channel to a user equipment
by a base station, the method comprising: transmitting first
transmission mode (TM) configuration information; transmitting a
first physical downlink channel based on the first TM configuration
information, wherein the first physical downlink channel has a
short transmission interval (TTI) duration equal to or short than a
duration of a slot in a time domain, wherein the first TM
configuration information includes information regarding a first TM
for the short TTI duration and information regarding the second TM
for the short TTI duration, wherein the first physical downlink
channel is transmitted based on the first TM when the first
physical downlink channel is transmitted in a multimedia broadcast
multicast service (MBSFN) subframe, and wherein the first physical
downlink channel is transmitted based on the second TM when the
first physical downlink channel is transmitted in a non-MBSFN
subframe.
14. The method according to claim 13, wherein the first TM is one
among a plurality of TMs which use a demodulation reference signal
(DMRS), and wherein the second TM is one among a plurality of TMs
which use the DMRS or cell-specific reference signal (CRS).
15. The method according to claim 13, further comprising:
transmitting a second physical downlink channel based on second TM
configuration information, wherein the second physical downlink
channel has a non-short TTI duration longer than the duration of
the slot in the time domain, wherein the second TM configuration
information includes information regarding one TM for the non-short
TTI duration, wherein the second physical downlink channel is
transmitted based on the one TM irrespective of whether the second
physical downlink channel is transmitted in the MBSFN subframe or
in the non-MBSFN subframe.
16. The method according to claim 13, wherein the duration of the
slot is 0.5 ms in the time domain.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] Pursuant to 35 U.S.C. .sctn. 119(e), this application claims
the benefit of U.S. Provisional Patent Application Nos. 62/266,000,
filed on Dec. 11, 2015, 62/335,653, filed on May 12, 2016,
62/335,703, filed on May 13, 2016, 62/401,935, filed on Sep. 30,
2016 and 62/405,216, filed on Oct. 6, 2016, the contents of which
are all hereby incorporated by reference herein in their
entirety.
TECHNICAL FIELD
[0002] The present invention relates to a wireless communication
system, and more particularly, to a method and apparatus for
transmitting/receiving a downlink signal.
BACKGROUND ART
[0003] With appearance and spread of machine-to-machine (M2M)
communication and a variety of devices such as smartphones and
tablet PCs and technology demanding a large amount of data
transmission, data throughput needed in a cellular network has
rapidly increased. To satisfy such rapidly increasing data
throughput, carrier aggregation technology, cognitive radio
technology, etc. for efficiently employing more frequency bands and
multiple input multiple output (MIMO) technology, multi-base
station (BS) cooperation technology, etc. for raising data capacity
transmitted on limited frequency resources have been developed.
[0004] A general wireless communication system performs data
transmission/reception through one downlink (DL) band and through
one uplink (UL) band corresponding to the DL band (in case of a
frequency division duplex (FDD) mode), or divides a prescribed
radio frame into a UL time unit and a DL time unit in the time
domain and then performs data transmission/reception through the
UL/DL time unit (in case of a time division duplex (TDD) mode). A
base station (BS) and a user equipment (UE) transmit and receive
data and/or control information scheduled on a prescribed time unit
basis, e.g. on a subframe basis. The data is transmitted and
received through a data region configured in a UL/DL subframe and
the control information is transmitted and received through a
control region configured in the UL/DL subframe. To this end,
various physical channels carrying radio signals are formed in the
UL/DL subframe. In contrast, carrier aggregation technology serves
to use a wider UL/DL bandwidth by aggregating a plurality of UL/DL
frequency blocks in order to use a broader frequency band so that
more signals relative to signals when a single carrier is used can
be simultaneously processed.
[0005] In addition, a communication environment has evolved into
increasing density of nodes accessible by a user at the periphery
of the nodes. A node refers to a fixed point capable of
transmitting/receiving a radio signal to/from the UE through one or
more antennas. A communication system including high-density nodes
may provide a better communication service to the UE through
cooperation between the nodes.
Technical Problem
[0006] Due to introduction of new radio communication technology,
the number of user equipments (UEs) to which a BS should provide a
service in a prescribed resource region increases and the amount of
data and control information that the BS should transmit to the UEs
increases. Since the amount of resources available to the BS for
communication with the UE(s) is limited, a new method in which the
BS efficiently receives/transmits uplink/downlink data and/or
uplink/downlink control information using the limited radio
resources is needed.
[0007] With development of technologies, overcoming delay or
latency has become an important challenge. Applications whose
performance critically depends on delay/latency are increasing.
Accordingly, a method to reduce delay/latency compared to the
legacy system is demanded.
[0008] Also, with development of smart devices, a new scheme for
efficiently transmitting/receiving a small amount of data or
efficiently transmitting/receiving data occurring at a low
frequency is required.
[0009] The technical objects that can be achieved through the
present invention are not limited to what has been particularly
described hereinabove and other technical objects not described
herein will be more clearly understood by persons skilled in the
art from the following detailed description.
SUMMARY
[0010] A downlink control channel and a downlink data channel
corresponding to the downlink control channel may be
transmitted/received within a transmission time interval (TTI). A
reference signal (RS) of one antenna port to be used for
transmission of both the downlink control channel and the downlink
data channel is transmitted/received within an OFDM symbol having
the downlink control channel among the OFDM symbols of the TTI, and
the RS of an antenna port used only for transmission of the
downlink data channel is transmitted within the remaining OFDM
symbol(s) of the TTI.
[0011] To achieve these objects and other advantages and in
accordance with the purpose of the invention, as embodied and
broadly described herein, a method of receiving a downlink channel
at a user equipment is provided. The method may include receiving a
first downlink control channel from a first antenna port within at
least one OFDM symbol of a first transmission time interval (TTI),
receiving a first downlink data channel corresponding to the first
downlink control channel from the first antenna port and a second
antenna port within remaining OFDM symbols of the first TTI,
receiving a first demodulation signal (DMRS) for the first antenna
port and a second DMRS for the second antenna port within the first
TTI, and demodulating the first downlink control channel based on
the first DMRS and demodulating the first downlink data channel
based on the first and second DMRSs. The first TTI may be
configured in a default TTI. The first TTI may be shorter than the
default TTI. The first DMRS may be received within the at least one
OFDM symbol having the first downlink control channel. The second
DMRS may be received within the remaining OFDM symbols.
[0012] In another aspect of the present invention, a method of
transmitting a downlink signal to a user equipment at a base
station is provided. The method may include transmitting a first
downlink control channel through a first antenna port within at
least one OFDM symbol of a first transmission time interval (TTI),
transmitting a first downlink data channel corresponding to the
first downlink control channel through the first antenna port and a
second antenna port within remaining OFDM symbols of the first TTI,
and transmitting a first demodulation signal (DMRS) for the first
antenna port and a second DMRS for the second antenna port within
the first TTI. The first TTI may be configured in a default TTI,
and is shorter than the default TTI. The first DMRS may be
transmitted within the at least one OFDM symbol having the first
downlink control channel. The second DMRS may be transmitted within
the remaining OFDM symbols.
[0013] In another aspect of the present invention, a user equipment
for receiving a downlink channel is provided. The user equipment
includes a radio frequency (RF) unit, and a processor configured to
control the RF unit. The processor may be configured to control the
RF unit to receive a first downlink control channel from a first
antenna port within at least one OFDM symbol of a first
transmission time interval (TTI). The processor may be configured
to control the RF unit to receive a first downlink data channel
corresponding to the first downlink control channel from the first
antenna port and a second antenna port within remaining OFDM
symbols of the first TTI. The processor may be configured to
control the RF unit to receive a first demodulation signal (DMRS)
for the first antenna port and a second DMRS for the second antenna
port within the first TTI. The processor may be configured to
demodulate the first downlink control channel based on the first
DMRS and demodulating the first downlink data channel based on the
first and second DMRSs. The first TTI may be configured in a
default TTI. The first TTI may be shorter than the default TTI. The
first DMRS may be received within the at least one OFDM symbol
having the first downlink control channel. The second DMRS may be
received within the remaining OFDM symbols.
[0014] In another aspect of the present invention, a base station
for transmitting a downlink signal to a user equipment is provided.
The base station includes a radio frequency (RF) unit, and a
processor configured to control the RF unit. The processor may be
configured to control the RF unit to transmit a first downlink
control channel through a first antenna port within at least one
OFDM symbol of a first transmission time interval (TTI). The
processor may be configured to control the RF unit to transmit a
first downlink data channel corresponding to the first downlink
control channel through the first antenna port and a second antenna
port within remaining OFDM symbols of the first TTI. The processor
may be configured to control the RF unit to transmit a first
demodulation signal (DMRS) for the first antenna port and a second
DMRS for the second antenna port within the first TTI. The first
TTI may be configured in a default TTI. The first TTI may be
shorter than the default TTI. The first DMRS may be transmitted
within the at least one OFDM symbol having the first downlink
control channel. The second DMRS may be transmitted within the
remaining OFDM symbols.
[0015] In each aspect of the present invention, the first TTI may
have a time length of 0.5 ms or less, and the default TTI may have
a time length of 1 ms.
[0016] In each aspect of the present invention, the first TTI may
include only orthogonal frequency division multiplexing (OFDM)
symbols without a cell-specific reference signal (CRS).
[0017] In each aspect of the present invention, a second downlink
control channel and a second downlink data channel corresponding to
the second downlink control channel may be further transmitted or
received in a second TTI including an OFDM symbol with a
cell-specific reference signal (CRS), the second TTI being
configured in the default TTI. The second downlink control channel
and the second downlink data channel may be transmitted or
demodulated based on the CRS.
[0018] In each aspect of the present invention, the first DMRS and
the second DMRS may be present only on a physical resource block
having the first downlink control channel or the first downlink
data channel among physical resource blocks having the first TTI
configured thereon.
[0019] According to the present invention, uplink/downlink signals
can be efficiently transmitted/received. Therefore, overall
throughput of a radio communication system can be improved.
[0020] According to one embodiment of the present invention, a low
cost/complexity UE can perform communication with a BS at low cost
while maintaining compatibility with a legacy system.
[0021] According to one embodiment of the present invention, the UE
can be implemented at low cost/complexity.
[0022] According to one embodiment of the present invention, the UE
and the BS can perform communication with each other at a
narrowband.
[0023] According to an embodiment of the present invention,
delay/latency occurring during communication between a user
equipment and a base station may be reduced.
[0024] According to an embodiment of the present invention, a small
amount of data may be efficiently transmitted/received.
BRIEF DESCRIPTION OF THE DRAWING
[0025] The accompanying drawings, which are included to provide a
further understanding of the invention, illustrate embodiments of
the invention and together with the description serve to explain
the principle of the invention.
[0026] FIG. 1 illustrates the structure of a radio frame used in a
wireless communication system.
[0027] FIG. 2 illustrates the structure of a downlink (DL)/uplink
(UL) slot in a wireless communication system.
[0028] FIG. 3 illustrates the structure of a DL subframe used in a
wireless communication system.
[0029] FIG. 4 illustrates the structure of a UL subframe used in a
wireless communication system.
[0030] FIG. 5 illustrates configuration of cell specific reference
signals (CRSs) and user specific reference signals (UE-RS).
[0031] FIG. 6 is a example of a downlink control channel configured
in a data region of a DL subframe.
[0032] FIG. 7 illustrates the length of a transmission time
interval (TTI) which is needed to implement low latency.
[0033] FIG. 8 illustrates an sTTI and transmission of a control
channel and data channel within the sTTI.
[0034] FIG. 9 illustrates an example of short TTIs configured in a
legacy subframe.
[0035] FIG. 10 illustrates another example of short TTIs configured
in a legacy subframe.
[0036] FIG. 11 illustrates a demodulation reference signal (DMRS)
within one OFDM symbol.
[0037] FIG. 12 illustrates examples of configuration of sTTI(s) in
consideration of the legacy PDCCH region and CRS.
[0038] FIGS. 13 to 38 illustrate RS structures according to an
embodiment of the present invention.
[0039] FIG. 39 is a block diagram illustrating elements of a
transmitting device 10 and a receiving device 20 for implementing
the present invention.
DETAILED DESCRIPTION
[0040] Reference will now be made in detail to the exemplary
embodiments of the present invention, examples of which are
illustrated in the accompanying drawings. The detailed description,
which will be given below with reference to the accompanying
drawings, is intended to explain exemplary embodiments of the
present invention, rather than to show the only embodiments that
can be implemented according to the invention. The following
detailed description includes specific details in order to provide
a thorough understanding of the present invention. However, it will
be apparent to those skilled in the art that the present invention
may be practiced without such specific details.
[0041] In some instances, known structures and devices are omitted
or are shown in block diagram form, focusing on important features
of the structures and devices, so as not to obscure the concept of
the present invention. The same reference numbers will be used
throughout this specification to refer to the same or like
parts.
[0042] The following techniques, apparatuses, and systems may be
applied to a variety of wireless multiple access systems. Examples
of the multiple access systems include a code division multiple
access (CDMA) system, a frequency division multiple access (FDMA)
system, a time division multiple access (TDMA) system, an
orthogonal frequency division multiple access (OFDMA) system, a
single carrier frequency division multiple access (SC-FDMA) system,
and a multicarrier frequency division multiple access (MC-FDMA)
system. CDMA may be embodied through radio technology such as
universal terrestrial radio access (UTRA) or CDMA2000. TDMA may be
embodied through radio technology such as global system for mobile
communications (GSM), general packet radio service (GPRS), or
enhanced data rates for GSM evolution (EDGE). OFDMA may be embodied
through radio technology such as institute of electrical and
electronics engineers (IEEE) 802.11 (Wi-Fi), IEEE 802.16 (WiMAX),
IEEE 802.20, or evolved UTRA (E-UTRA). UTRA is a part of a
universal mobile telecommunications system (UMTS). 3rd generation
partnership project (3GPP) long term evolution (LTE) is a part of
evolved UMTS (E-UMTS) using E-UTRA. 3GPP LTE employs OFDMA in DL
and SC-FDMA in UL. LTE-advanced (LTE-A) is an evolved version of
3GPP LTE. For convenience of description, it is assumed that the
present invention is applied to 3GPP LTE/LTE-A. However, the
technical features of the present invention are not limited
thereto. For example, although the following detailed description
is given based on a mobile communication system corresponding to a
3GPP LTE/LTE-A system, aspects of the present invention that are
not specific to 3GPP LTE/LTE-A are applicable to other mobile
communication systems.
[0043] For example, the present invention is applicable to
contention based communication such as Wi-Fi as well as
non-contention based communication as in the 3GPP LTE/LTE-A system
in which an eNB allocates a DL/UL time/frequency resource to a UE
and the UE receives a DL signal and transmits a UL signal according
to resource allocation of the eNB. In a non-contention based
communication scheme, an access point (AP) or a control node for
controlling the AP allocates a resource for communication between
the UE and the AP, whereas, in a contention based communication
scheme, a communication resource is occupied through contention
between UEs which desire to access the AP. The contention based
communication scheme will now be described in brief. One type of
the contention based communication scheme is carrier sense multiple
access (CSMA). CSMA refers to a probabilistic media access control
(MAC) protocol for confirming, before a node or a communication
device transmits traffic on a shared transmission medium (also
called a shared channel) such as a frequency band, that there is no
other traffic on the same shared transmission medium. In CSMA, a
transmitting device determines whether another transmission is
being performed before attempting to transmit traffic to a
receiving device. In other words, the transmitting device attempts
to detect presence of a carrier from another transmitting device
before attempting to perform transmission. Upon sensing the
carrier, the transmitting device waits for another transmission
device which is performing transmission to finish transmission,
before performing transmission thereof. Consequently, CSMA can be a
communication scheme based on the principle of "sense before
transmit" or "listen before talk". A scheme for avoiding collision
between transmitting devices in the contention based communication
system using CSMA includes carrier sense multiple access with
collision detection (CSMA/CD) and/or carrier sense multiple access
with collision avoidance (CSMA/CA). CSMA/CD is a collision
detection scheme in a wired local area network (LAN) environment.
In CSMA/CD, a personal computer (PC) or a server which desires to
perform communication in an Ethernet environment first confirms
whether communication occurs on a network and, if another device
carries data on the network, the PC or the server waits and then
transmits data. That is, when two or more users (e.g. PCs, UEs,
etc.) simultaneously transmit data, collision occurs between
simultaneous transmission and CSMA/CD is a scheme for flexibly
transmitting data by monitoring collision. A transmitting device
using CSMA/CD adjusts data transmission thereof by sensing data
transmission performed by another device using a specific rule.
CSMA/CA is a MAC protocol specified in IEEE 802.11 standards. A
wireless LAN (WLAN) system conforming to IEEE 802.11 standards does
not use CSMA/CD which has been used in IEEE 802.3 standards and
uses CA, i.e. a collision avoidance scheme. Transmission devices
always sense carrier of a network and, if the network is empty, the
transmission devices wait for determined time according to
locations thereof registered in a list and then transmit data.
Various methods are used to determine priority of the transmission
devices in the list and to reconfigure priority. In a system
according to some versions of IEEE 802.11 standards, collision may
occur and, in this case, a collision sensing procedure is
performed. A transmission device using CSMA/CA avoids collision
between data transmission thereof and data transmission of another
transmission device using a specific rule.
[0044] In the present invention, a user equipment (UE) may be a
fixed or mobile device. Examples of the UE include various devices
that transmit and receive user data and/or various kinds of control
information to and from a base station (BS). The UE may be referred
to as a terminal equipment (TE), a mobile station (MS), a mobile
terminal (MT), a user terminal (UT), a subscriber station (SS), a
wireless device, a personal digital assistant (PDA), a wireless
modem, a handheld device, etc. In addition, in the present
invention, a BS generally refers to a fixed station that performs
communication with a UE and/or another BS, and exchanges various
kinds of data and control information with the UE and another BS.
The BS may be referred to as an advanced base station (ABS), a
node-B (NB), an evolved node-B (eNB), a base transceiver system
(BTS), an access point (AP), a processing server (PS), etc. In
describing the present invention, a BS will be referred to as an
eNB.
[0045] In the present invention, a node refers to a fixed point
capable of transmitting/receiving a radio signal through
communication with a UE. Various types of eNBs may be used as nodes
irrespective of the terms thereof. For example, a BS, a node B
(NB), an e-node B (eNB), a pico-cell eNB (PeNB), a home eNB (HeNB),
a relay, a repeater, etc. may be a node. In addition, the node may
not be an eNB. For example, the node may be a radio remote head
(RRH) or a radio remote unit (RRU). The RRH or RRU generally has a
lower power level than a power level of an eNB. Since the RRH or
RRU (hereinafter, RRH/RRU) is generally connected to the eNB
through a dedicated line such as an optical cable, cooperative
communication between RRH/RRU and the eNB can be smoothly performed
in comparison with cooperative communication between eNBs connected
by a radio line. At least one antenna is installed per node. The
antenna may mean a physical antenna or mean an antenna port or a
virtual antenna.
[0046] In the present invention, a cell refers to a prescribed
geographical area to which one or more nodes provide a
communication service. Accordingly, in the present invention,
communicating with a specific cell may mean communicating with an
eNB or a node which provides a communication service to the
specific cell. In addition, a DL/UL signal of a specific cell
refers to a DL/UL signal from/to an eNB or a node which provides a
communication service to the specific cell. A node providing UL/DL
communication services to a UE is called a serving node and a cell
to which UL/DL communication services are provided by the serving
node is especially called a serving cell. Furthermore, channel
status/quality of a specific cell refers to channel status/quality
of a channel or communication link formed between an eNB or node
which provides a communication service to the specific cell and a
UE. The UE may measure DL channel state received from a specific
node using cell-specific reference signal(s) (CRS(s)) transmitted
on a CRS resource and/or channel state information reference
signal(s) (CSI-RS(s)) transmitted on a CSI-RS resource, allocated
by antenna port(s) of the specific node to the specific node.
Detailed CSI-RS configuration may be understood with reference to
3GPP TS 36.211 and 3GPP TS 36.331 documents.
[0047] Meanwhile, a 3GPP LTE/LTE-A system uses the concept of a
cell in order to manage radio resources and a cell associated with
the radio resources is distinguished from a cell of a geographic
region.
[0048] A "cell" of a geographic region may be understood as
coverage within which a node can provide service using a carrier
and a "cell" of a radio resource is associated with bandwidth (BW)
which is a frequency range configured by the carrier. Since DL
coverage, which is a range within which the node is capable of
transmitting a valid signal, and UL coverage, which is a range
within which the node is capable of receiving the valid signal from
the UE, depends upon a carrier carrying the signal, the coverage of
the node may be associated with coverage of the "cell" of a radio
resource used by the node. Accordingly, the term "cell" may be used
to indicate service coverage of the node sometimes, a radio
resource at other times, or a range that a signal using a radio
resource can reach with valid strength at other times. The "cell"
of the radio resource will be described later in more detail.
[0049] 3GPP LTE/LTE-A standards define DL physical channels
corresponding to resource elements carrying information derived
from a higher layer and DL physical signals corresponding to
resource elements which are used by a physical layer but which do
not carry information derived from a higher layer. For example, a
physical downlink shared channel (PDSCH), a physical broadcast
channel (PBCH), a physical multicast channel (PMCH), a physical
control format indicator channel (PCFICH), a physical downlink
control channel (PDCCH), and a physical hybrid ARQ indicator
channel (PHICH) are defined as the DL physical channels, and a
reference signal and a synchronization signal are defined as the DL
physical signals. A reference signal (RS), also called a pilot,
refers to a special waveform of a predefined signal known to both a
BS and a UE. For example, a cell-specific RS (CRS), a UE-specific
RS (UE-RS), a positioning RS (PRS), and channel state information
RS (CSI-RS) may be defined as DL RSs. Meanwhile, the 3GPP LTE/LTE-A
standards define UL physical channels corresponding to resource
elements carrying information derived from a higher layer and UL
physical signals corresponding to resource elements which are used
by a physical layer but which do not carry information derived from
a higher layer. For example, a physical uplink shared channel
(PUSCH), a physical uplink control channel (PUCCH), and a physical
random access channel (PRACH) are defined as the UL physical
channels, and a demodulation reference signal (DM RS) for a UL
control/data signal and a sounding reference signal (SRS) used for
UL channel measurement are defined as the UL physical signals.
[0050] In the present invention, a physical downlink control
channel (PDCCH), a physical control format indicator channel
(PCFICH), a physical hybrid automatic retransmit request indicator
channel (PHICH), and a physical downlink shared channel (PDSCH)
refer to a set of time-frequency resources or resource elements
(REs) carrying downlink control information (DCI), a set of
time-frequency resources or REs carrying a control format indicator
(CFI), a set of time-frequency resources or REs carrying downlink
acknowledgement (ACK)/negative ACK (NACK), and a set of
time-frequency resources or REs carrying downlink data,
respectively. In addition, a physical uplink control channel
(PUCCH), a physical uplink shared channel (PUSCH) and a physical
random access channel (PRACH) refer to a set of time-frequency
resources or REs carrying uplink control information (UCI), a set
of time-frequency resources or REs carrying uplink data and a set
of time-frequency resources or REs carrying random access signals,
respectively. In the present invention, in particular, a
time-frequency resource or RE that is assigned to or belongs to
PDCCH/PCFICH/PHICH/PDSCH/PUCCH/PUSCH/PRACH is referred to as
PDCCH/PCFICH/PHICH/PDSCH/PUCCH/PUSCH/PRACH RE or
PDCCH/PCFICH/PHICH/PDSCH/PUCCH/PUSCH/PRACH time-frequency resource,
respectively. Therefore, in the present invention,
PUCCH/PUSCH/PRACH transmission of a UE is conceptually identical to
UCI/uplink data/random access signal transmission on
PUSCH/PUCCH/PRACH, respectively. In addition,
PDCCH/PCFICH/PHICH/PDSCH transmission of an eNB is conceptually
identical to downlink data/DCI transmission on
PDCCH/PCFICH/PHICH/PDSCH, respectively.
[0051] Hereinafter, OFDM symbol/subcarrier/RE to or for which
CRS/DMRS/CSI-RS/SRS/UE-RS/TRS is assigned or configured will be
referred to as CRS/DMRS/CSI-RS/SRS/UE-RS/TRS
symbol/carrier/subcarrier/RE. For example, an OFDM symbol to or for
which a tracking RS (TRS) is assigned or configured is referred to
as a TRS symbol, a subcarrier to or for which the TRS is assigned
or configured is referred to as a TRS subcarrier, and an RE to or
for which the TRS is assigned or configured is referred to as a TRS
RE. In addition, a subframe configured for transmission of the TRS
is referred to as a TRS subframe. Moreover, a subframe in which a
broadcast signal is transmitted is referred to as a broadcast
subframe or a PBCH subframe and a subframe in which a
synchronization signal (e.g. PSS and/or SSS) is transmitted is
referred to a synchronization signal subframe or a PSS/SSS
subframe. OFDM symbol/subcarrier/RE to or for which PSS/SSS is
assigned or configured is referred to as PSS/SSS
symbol/subcarrier/RE, respectively.
[0052] In the present invention, a CRS port, a UE-RS port, a CSI-RS
port, and a TRS port refer to an antenna port configured to
transmit a CRS, an antenna port configured to transmit a UE-RS, an
antenna port configured to transmit a CSI-RS, and an antenna port
configured to transmit a TRS, respectively. Antenna ports
configured to transmit CRSs may be distinguished from each other by
the locations of REs occupied by the CRSs according to CRS ports,
antenna ports configured to transmit UE-RSs may be distinguished
from each other by the locations of REs occupied by the UE-RSs
according to UE-RS ports, and antenna ports configured to transmit
CSI-RSs may be distinguished from each other by the locations of
REs occupied by the CSI-RSs according to CSI-RS ports. Therefore,
the term CRS/UE-RS/CSI-RS/TRS ports may also be used to indicate a
pattern of REs occupied by CRSs/UE-RSs/CSI-RSs/TRSs in a
predetermined resource region. In the present invention, both a
DMRS and a UE-RS refer to RSs for demodulation and, therefore, the
terms DMRS and UE-RS are used to refer to RSs for demodulation.
[0053] For terms and technologies which are not specifically
described among the terms of and technologies employed in this
specification, 3GPP LTE/LTE-A standard documents, for example, 3GPP
TS 36.211, 3GPP TS 36.212, 3GPP TS 36.213, 3GPP TS 36.321 and 3GPP
TS 36.331 may be referenced.
[0054] FIG. 1 illustrates the structure of a radio frame used in a
wireless communication system.
[0055] Specifically, FIG. 1(a) illustrates an exemplary structure
of a radio frame which can be used in frequency division
multiplexing (FDD) in 3GPP LTE/LTE-A and FIG. 1(b) illustrates an
exemplary structure of a radio frame which can be used in time
division multiplexing (TDD) in 3GPP LTE/LTE-A.
[0056] Referring to FIG. 1, a 3GPP LTE/LTE-A radio frame is 10 ms
(307,200T.sub.s) in duration. The radio frame is divided into 10
subframes of equal size. Subframe numbers may be assigned to the 10
subframes within one radio frame, respectively. Here, T.sub.s
denotes sampling time where T.sub.s=1/(2048*15 kHz). Each subframe
is 1 ms long and is further divided into two slots. 20 slots are
sequentially numbered from 0 to 19 in one radio frame. Duration of
each slot is 0.5 ms. A time interval in which one subframe is
transmitted is defined as a transmission time interval (TTI). Time
resources may be distinguished by a radio frame number (or radio
frame index), a subframe number (or subframe index), a slot number
(or slot index), and the like.
[0057] A TTI refers to an interval at which data may be scheduled.
For example, referring to FIGS. 1 and 3, the transmission
opportunity of a UL grant or DL grant is given every 1 ms in the
current LTE/LTE-A system. The UL/DL grant opportunity is not given
several times within a time shorter than 1 ms. Accordingly, the TTI
is 1 ms in the current LTE-LTE-A system.
[0058] A radio frame may have different configurations according to
duplex modes. In FDD mode for example, since DL transmission and UL
transmission are discriminated according to frequency, a radio
frame for a specific frequency band operating on a carrier
frequency includes either DL subframes or UL subframes. In TDD
mode, since DL transmission and UL transmission are discriminated
according to time, a radio frame for a specific frequency band
operating on a carrier frequency includes both DL subframes and UL
subframes.
[0059] TABLE 1 shows an exemplary UL-DL configuration within a
radio frame in TDD mode.
TABLE-US-00001 TABLE 1 Uplink- Downlink- downlink to-Uplink config-
Switch-point Subframe number uration periodicity 0 1 2 3 4 5 6 7 8
9 0 5 ms D S U U U D S U U U 1 5 ms D S U U D D S U U D 2 5 ms D S
U D D D S U D D 3 10 ms D S U U U D D D D D 4 10 ms D S U U D D D D
D D 5 10 ms D S U D D D D D D D 6 5 ms D S U U U D S U U D
[0060] In TABLE 1, D denotes a DL subframe, U denotes a UL
subframe, and S denotes a special subframe. The special subframe
includes three fields, i.e. downlink pilot time slot (DwPTS), guard
period (GP), and uplink pilot time slot (UpPTS). DwPTS is a time
slot reserved for DL transmission and UpPTS is a time slot reserved
for UL transmission. TABLE 2 shows an example of the special
subframe configuration.
TABLE-US-00002 TABLE 2 Normal cyclic prefix in downlink Extended
cyclic prefix in downlink UpPTS UpPTS Special subframe Normal
cyclic Extended cyclic Normal cyclic Extended cyclic configuration
DwPTS prefix in uplink prefix in uplink DwPTS prefix in uplink
prefix in uplink 0 6592 T.sub.s 2192 T.sub.s 2560 T.sub.s 7680
T.sub.s 2192 T.sub.s 2560 T.sub.s 1 19760 T.sub.s 20480 T.sub.s 2
21952 T.sub.s 23040 T.sub.s 3 24144 T.sub.s 25600 T.sub.s 4 26336
T.sub.s 7680 T.sub.s 4384 T.sub.s 5120 T.sub.s 5 6592 T.sub.s 4384
T.sub.s 5120 T.sub.s 20480 T.sub.s 6 19760 T.sub.s 23040 T.sub.s 7
21952 T.sub.s 12800 T.sub.s 8 24144 T.sub.s -- -- -- 9 13168
T.sub.s --
[0061] FIG. 2 illustrates the structure of a DL/UL slot structure
in a wireless communication system.
[0062] Referring to FIG. 2, a slot includes a plurality of
orthogonal frequency division multiplexing (OFDM) symbols in the
time domain and includes a plurality of resource blocks (RBs) in
the frequency domain. The OFDM symbol may refer to one symbol
duration. Referring to FIG. 2, a signal transmitted in each slot
may be expressed by a resource grid including
N.sup.DL/UL.sub.RB*N.sup.RB.sub.sc subcarriers and
N.sup.DL/UL.sub.symb OFDM symbols. N.sup.DL.sub.RB denotes the
number of RBs in a DL slot and N.sup.UL.sub.RB denotes the number
of RBs in a UL slot. N.sup.DL.sub.RB and N.sup.UL.sub.RB depend on
a DL transmission bandwidth and a UL transmission bandwidth,
respectively. N.sup.DL.sub.symb denotes the number of OFDM symbols
in a DL slot, N.sup.UL.sub.symb denotes the number of OFDM symbols
in a UL slot, and N.sup.RB.sub.sc denotes the number of subcarriers
configuring one RB.
[0063] An OFDM symbol may be referred to as an OFDM symbol, a
single carrier frequency division multiplexing (SC-FDM) symbol,
etc. according to multiple access schemes. The number of OFDM
symbols included in one slot may be varied according to channel
bandwidths and CP lengths. For example, in a normal cyclic prefix
(CP) case, one slot includes 7 OFDM symbols. In an extended CP
case, one slot includes 6 OFDM symbols. Although one slot of a
subframe including 7 OFDM symbols is shown in FIG. 2 for
convenience of description, embodiments of the present invention
are similarly applicable to subframes having a different number of
OFDM symbols. Referring to FIG. 2, each OFDM symbol includes
N.sup.DL/UL.sub.RB*N.sup.RB.sub.sc subcarriers in the frequency
domain. The type of the subcarrier may be divided into a data
subcarrier for data transmission, a reference signal (RS)
subcarrier for RS transmission, and a null subcarrier for a guard
band and a DC component. The null subcarrier for the DC component
is unused and is mapped to a carrier frequency f.sub.0 in a process
of generating an OFDM signal or in a frequency up-conversion
process. The carrier frequency is also called a center frequency
f.sub.c.
[0064] One RB is defined as N.sup.DL/UL.sub.symb (e.g. 7)
consecutive OFDM symbols in the time domain and as N.sup.RB.sub.sc
(e.g. 12) consecutive subcarriers in the frequency domain. For
reference, a resource composed of one OFDM symbol and one
subcarrier is referred to a resource element (RE) or tone.
Accordingly, one RB includes N.sup.DL/UL.sub.symb*N.sup.RB.sub.sc
REs. Each RE within a resource grid may be uniquely defined by an
index pair (k, l) within one slot. k is an index ranging from 0 to
N.sup.DL/UL.sub.RB*N.sup.RB.sub.sc-1 in the frequency domain, and l
is an index ranging from 0 to N.sup.DL/UL.sub.symb-1 in the time
domain.
[0065] Meanwhile, one RB is mapped to one physical resource block
(PRB) and one virtual resource block (VRB). A PRB is defined as
N.sup.DL.sub.symb (e.g. 7) consecutive OFDM or SC-FDM symbols in
the time domain and N.sup.RB.sub.sc (e.g. 12) consecutive
subcarriers in the frequency domain. Accordingly, one PRB is
configured with N.sup.DL/UL.sub.symb*N.sup.RB.sub.sc REs. In one
subframe, two RBs each located in two slots of the subframe while
occupying the same N.sup.RB.sub.sc consecutive subcarriers are
referred to as a physical resource block (PRB) pair. Two RBs
configuring a PRB pair have the same PRB number (or the same PRB
index).
[0066] FIG. 3 illustrates the structure of a DL subframe used in a
wireless communication system.
[0067] Referring to FIG. 3, a DL subframe is divided into a control
region and a data region in the time domain. Referring to FIG. 3, a
maximum of 3 (or 4) OFDM symbols located in a front part of a first
slot of a subframe corresponds to the control region. Hereinafter,
a resource region for PDCCH transmission in a DL subframe is
referred to as a PDCCH region. OFDM symbols other than the OFDM
symbol(s) used in the control region correspond to the data region
to which a physical downlink shared channel (PDSCH) is allocated.
Hereinafter, a resource region available for PDSCH transmission in
the DL subframe is referred to as a PDSCH region.
[0068] Examples of a DL control channel used in 3GPP LTE include a
physical control format indicator channel (PCFICH), a physical
downlink control channel (PDCCH), a physical hybrid ARQ indicator
channel (PHICH), etc.
[0069] The PCFICH is transmitted in the first OFDM symbol of a
subframe and carries information about the number of OFDM symbols
available for transmission of a control channel within a subframe.
The PCFICH notifies the UE of the number of OFDM symbols used for
the corresponding subframe every subframe. The PCFICH is located at
the first OFDM symbol. The PCFICH is configured by four resource
element groups (REGs), each of which is distributed within a
control region on the basis of cell ID. One REG includes four REs.
A set of OFDM symbols available for the PDCCH at a subframe is
given by the following Table.
TABLE-US-00003 TABLE 3 Number Number of OFDM of OFDM symbols
symbols for PDCCH for PDCCH when when Subframe N.sup.DL.sub.RB >
10 N.sup.DL.sub.RB .ltoreq. 10 Subframe 1 and 6 for frame structure
type 2 1, 2 2 MBSFN subframes on a carrier supporting 1, 2 2 PDSCH,
configured with 1 or 2 cell-specfic antenna ports MBSFN subframes
on a carrier supporting 2 2 PDSCH, configured with 4 cell-specific
antenna ports Subframes on a carrier not 0 0 supporting PDSCH
Non-MBSFN subframes (except subframe 6 1, 2, 3 2, 3 for frame
structure type 2) configured with positioning reference signals All
other cases 1, 2, 3 2, 3, 4
[0070] A subset of downlink subframes within a radio frame on a
carrier for supporting PDSCH transmission may be configured as
MBSFN subframe(s) by a higher layer. Each MBSFN subframe is divided
into a non-MBSFN region and an MBSFN region. The non-MBSFN region
spans first one or two OFDM symbols, and its length is given by
TABLE 3. The same CP as cyclic prefix (CP) used for subframe 0 is
used for transmission within the non-MBSFN region of the MBSFN
subframe. The MBSFN region within the MBSFN subframe is defined as
OFDM symbols which are not used in the non-MBSFN region.
[0071] The PCFICH carries a control format indicator (CFI), which
indicates any one of values of 1 to 3. For a downlink system
bandwidth N.sup.DL.sub.RB>10, the number 1, 2 or 3 of OFDM
symbols which are spans of DCI carried by the PDCCH is given by the
CFI. For a downlink system bandwidth N.sup.DL.sub.RB.ltoreq.10, the
number 2, 3 or 4 of OFDM symbols which are spans of DCI carried by
the PDCCH is given by CFI+1. The CFI is coded in accordance with
the following Table.
TABLE-US-00004 TABLE 4 CFI code word CFI <b.sub.0, b.sub.1, . .
. , b.sub.31> 1 <0, 1, 1, 0, 1, 1, 0, 1, 1, 0, 1, 1, 0, 1, 1,
0, 1, 1, 0, 1, 1, 0, 1, 1, 0, 1, 1, 0, 1, 1, 0, 1> 2 <1, 0,
1, 1, 0, 1, 1, 0, 1, 1, 0, 1, 1, 0, 1, 1, 0, 1, 1, 0, 1, 1, 0, 1,
1, 0, 1, 1, 0, 1, 1, 0> 3 <1, 1, 0, 1, 1, 0, 1, 1, 0, 1, 1,
0, 1, 1, 0, 1, 1, 0, 1, 1, 0, 1, 1, 0, 1, 1, 0, 1, 1, 0, 1, 1> 4
<0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, (Reserved) 0, 0, 0, 0, 0, 0, 0, 0, 0, 0>
[0072] The PHICH carries a HARQ (Hybrid Automatic Repeat Request)
ACK/NACK (acknowledgment/negative-acknowledgment) signal as a
response to UL transmission. The PHICH includes three REGs, and is
scrambled cell-specifically. ACK/NACK is indicated by 1 bit, and
the ACK/NACK of 1 bit is repeated three times. Each of the repeated
ACK/NACK bits is spread with a spreading factor (SF) 4 or 2 and
then mapped into a control region.
[0073] The control information transmitted through the PDCCH will
be referred to as downlink control information (DCI). The DCI
includes resource allocation information for a UE or UE group and
other control information. Transmit format and resource allocation
information of a downlink shared channel (DL-SCH) are referred to
as DL scheduling information or DL grant. Transmit format and
resource allocation information of an uplink shared channel
(UL-SCH) are referred to as UL scheduling information or UL grant.
The size and usage of the DCI carried by one PDCCH are varied
depending on DCI formats. The size of the DCI may be varied
depending on a coding rate. In the current 3GPP LTE system, various
formats are defined, wherein formats 0 and 4 are defined for a UL,
and formats 1, 1A, 1B, 1C, 1D, 2, 2A, 2B, 2C, 3 and 3A are defined
for a DL. Combination selected from control information such as a
hopping flag, RB allocation, modulation coding scheme (MCS),
redundancy version (RV), new data indicator (NDI), transmit power
control (TPC), cyclic shift, cyclic shift demodulation reference
signal (DM RS), UL index, channel quality information (CQI)
request, DL assignment index, HARQ process number, transmitted
precoding matrix indicator (TPMI), precoding matrix indicator (PMI)
information is transmitted to the UE as the DCI. The following
table shows examples of DCI formats.
TABLE-US-00005 TABLE 5 DCI format Description 0 Resource grants for
the PUSCH transmissions (uplink) 1 Resource assignments for single
codeword PDSCH transmissions 1A Compact signaling of resource
assignments for single codeword PDSCH 1B Compact signaling of
resource assignments for single codeword PDSCH 1C Very compact
resource assignments for PDSCH (e.g. paging/ broadcast system
information) 1D Compact resource assignments for PDSCH using
multi-user MIMO 2 Resource assignments for PDSCH for closed-loop
MIMO operation 2A Resource assignments for PDSCH for open-loop MIMO
operation 2B Resource assignments for PDSCH using up to 2 antenna
ports with UE-specific reference signals 2C Resource assignment for
PDSCH using up to 8 antenna ports with UE-specific reference
signals 3/3A Power control commands for PUCCH and PUSCH with
2-bit/1-bit power adjustments 4 Scheduling of PUSCH in one UL
Component Carrier with multi- antenna port transmission mode
[0074] Other DCI formats in addition to the DCI formats defined in
TABLE 5 may be defined.
[0075] A plurality of PDCCHs may be transmitted within a control
region. A UE may monitor the plurality of PDCCHs. An eNB determines
a DCI format depending on the DCI to be transmitted to the UE, and
attaches cyclic redundancy check (CRC) to the DCI. The CRC is
masked (or scrambled) with an identifier (for example, a radio
network temporary identifier (RNTI)) depending on usage of the
PDCCH or owner of the PDCCH. For example, if the PDCCH is for a
specific UE, the CRC may be masked with an identifier (for example,
cell-RNTI (C-RNTI)) of the corresponding UE. If the PDCCH is for a
paging message, the CRC may be masked with a paging identifier (for
example, paging-RNTI (P-RNTI)). If the PDCCH is for system
information (in more detail, system information block (SIB)), the
CRC may be masked with system information RNTI (SI-RNTI). If the
PDCCH is for a random access response, the CRC may be masked with a
random access RNTI (RA-RNTI). For example, CRC masking (or
scrambling) includes XOR operation of CRC and RNTI at the bit
level.
[0076] Generally, a DCI format, which may be transmitted to the UE,
is varied depending on a transmission mode configured for the UE.
In other words, certain DCI format(s) corresponding to the specific
transmission mode not all DCI formats may only be used for the UE
configured to a specific transmission mode. The DCI formats that
the UE shall monitor depend on the configured transmission mode per
each serving cell. TABLE 6 illustrates transmission modes for
configuring multi-antenna technology and DCI formats for allowing a
UE to perform blind decoding at the corresponding transmission
mode. Particularly, TABLE 6 illustrates a relation between PDCCH
and PDSCH configured by C-RNTI (Cell RNTI(Radio Network Temporary
Identifier)).
TABLE-US-00006 TABLE 6 Transmission Transmission scheme of PDSCH
mode DCI format Search Space corresponding to PDCCH Mode 1 DCI
format Common and Single-antenna port, port 0 1A UE specific by C-
RNTI DCI format 1 UE specific by C- Single-antenna port, port 0
RNTI Mode 2 DCI format Common and Transmit diversity 1A UE specific
by C- RNTI DCI format 1 UE specific by C- Transmit diversity RNTI
Mode 3 DCI format Common and Transmit diversity 1A UE specific by
C- RNTI DCI format UE specific by C- Large delay CDD or Transmit 2A
RNTI diversity Mode 4 DCI format Common and Transmit diversity 1A
UE specific by C- RNTI DCI format 2 UE specific by C- Closed-loop
spatial multiplexing or RNTI Transmit diversity Mode 5 DCI format
Common and Transmit diversity 1A UE specific by C- RNTI DCI format
UE specific by C- Multi-user MIMO 1D RNTI Mode 6 DCI format Common
and Transmit diversity 1A UE specific by C- RNTI DCI format UE
specific by C- Closed-loop spatial multiplexing using 1B RNTI a
single transmission layer Mode 7 DCI format Common and If the
number of PBCH antenna ports 1A UE specific by C- is one,
Single-antenna port, port 0 is RNTI used, otherwise Transmit
diversity DCI format 1 UE specific by C- Single-antenna port, port
5 RNTI Mode 8 DCI format Common and If the number of PBCH antenna
ports 1A UE specific by C- is one, Single-antenna port, port 0 is
RNTI used, otherwise Transmit diversity DCI format UE specific by
C- Dual layer transmission, port 7 and 8 2B RNTI or single-antenna
port, port 7 or 8 Mode 9 DCI format Common and UE Non-MBSFN
subframe: If the 1A specific by C-RNTI number of PBCH antenna ports
is one, Single-antenna port, port 0 is used, otherwise Transmit
diversity MBSFN subframe: Single-antenna port, port 7 DCI format UE
specific by C- Up to 8 layer transmission, ports 7-14 2C RNTI or
single-antenna port, port 7 or 8 Mode 10 DCI format Common and UE
Non-MBSFN subframe: If the 1A specific by C-RNTI number of PBCH
antenna ports is one, Single-antenna port, port 0 is used,
otherwise Transmit diversity MBSFN subframe: Single-antenna port,
port 7 DCI format UE specific by C- Up to 8 layer transmission,
ports 7-14 2D RNTI or single-antenna port, port 7 or 8
[0077] Although transmission modes 1 to 10 are listed in TABLE 6,
other transmission modes in addition to the transmission modes
defined in TABLE 6 may be defined.
[0078] Referring to TABLE 6, a UE configured to a transmission mode
9, for example, tries to decode PDCCH candidates of a UE-specific
search space (USS) to a DCI format 1A, and tries to decode PDCCH
candidates of a common search space (CSS) and the USS to a DCI
format 2C. The UE may decode a PDSCH in accordance with DCI based
on the DCI format successfully decoded. If DCI decoding from one of
a plurality of PDCCH candidates to the DCI format 1A is
successfully performed, the UE may decode the PDSCH by assuming
that up to 8 layers from antenna ports 7 to 14 are transmitted
thereto through the PDSCH, or may decode the PDSCH by assuming that
a single layer from the antenna port 7 or 8 is transmitted thereto
through the PDSCH.
[0079] For example, a transmission mode is semi-statically
configured for the UE to allow the UE to receive a PDSCH which is
transmitted according to one of a plurality of predefined
transmission modes. The UE attempts to decode the PDCCH using only
DCI formats corresponding to the transmission mode thereof. In
other words, in order to maintain the computational load of the UE
according to an attempt of blind decoding at a level lower than or
equal to a certain level, not all DCI formats are simultaneously
searched by the UE.
[0080] The PDCCH is allocated to first m number of OFDM symbol(s)
within a subframe. In this case, m is an integer equal to or
greater than 1, and is indicated by the PCFICH.
[0081] The PDCCH is transmitted on an aggregation of one or a
plurality of continuous control channel elements (CCEs). The CCE is
a logic allocation unit used to provide a coding rate based on the
status of a radio channel to the PDCCH. The CCE corresponds to a
plurality of resource element groups (REGs). For example, each CCE
contains 9 REGs, which are distributed across the first 1/2/3 (/4
if needed for a 1.4 MHz channel) OFDM symbols and the system
bandwidth through interleaving to enable diversity and to mitigate
interference. One REG corresponds to four REs. Four QPSK symbols
are mapped to each REG. A resource element (RE) occupied by the
reference signal (RS) is not included in the REG. Accordingly, the
number of REGs within given OFDM symbols is varied depending on the
presence of the RS. The REGs are also used for other downlink
control channels (that is, PDFICH and PHICH).
[0082] Assuming that the number of REGs not allocated to the PCFICH
or the PHICH is N.sub.REG, the number of available CCEs in a DL
subframe for PDCCH(s) in a system is numbered from 0 to
N.sub.CCE-1, where N.sub.CCE=floor(N.sub.REG/9). The control region
of each serving cell consists of a set of CCEs, numbered from 0 to
N.sub.CCE,k-1, where N.sub.CCE,k is the total number of CCEs in the
control region of subframe k. A PDCCH consisting of n consecutive
CCEs may only start on a CCE fulfilling i mod n=0, where i is the
CCE number.
[0083] A PDCCH format and the number of DCI bits are determined in
accordance with the number of CCEs. The CCEs are numbered and
consecutively used. To simplify the decoding process, a PDCCH
having a format including n CCEs may be initiated only on CCEs
assigned numbers corresponding to multiples of n. The number of
CCEs used for transmission of a specific PDCCH is determined by a
network or the eNB in accordance with channel status. For example,
one CCE may be required for a PDCCH for a UE (for example, adjacent
to eNB) having a good downlink channel. However, in case of a PDCCH
for a UE (for example, located near the cell edge) having a poor
channel, eight CCEs may be required to obtain sufficient
robustness. Additionally, a power level of the PDCCH may be
adjusted to correspond to a channel status.
[0084] In a 3GPP LTE/LTE-A system, a set of CCEs on which a PDCCH
can be located for each UE is defined. A CCE set in which the UE
can detect a PDCCH thereof is referred to as a PDCCH search space
or simply as a search space (SS). An individual resource on which
the PDCCH can be transmitted in the SS is called a PDCCH candidate.
A set of PDCCH candidates that the UE is to monitor is defined in
terms of SSs, where a search space S.sup.(L).sub.k at aggregation
level L.di-elect cons.{1,2,4,8} is defined by a set of PDCCH
candidates. SSs for respective PDCCH formats may have different
sizes and a dedicated SS and a common SS are defined. The dedicated
SS is a UE-specific SS (USS) and is configured for each individual
UE. The common SS (CSS) is configured for a plurality of UEs. The
following table shows an example of aggregation levels for defining
SS.
TABLE-US-00007 TABLE 7 Search space S.sup.(L).sub.k Number of PDCCH
Type Aggregation level L Size [in CCEs] candidates M.sup.(L)
UE-specific 1 6 6 2 12 6 4 8 2 8 16 2 Common 4 16 4 8 16 2
[0085] For each serving cell on which PDCCH is monitored, the CCEs
corresponding to PDCCH candidates m of the search space
S.sup.(L).sub.k are configured by "L*{(Y.sub.k+m') mod
floor(N.sub.CCE,k/L)}+i", where i=0, . . . , L-1. For the common
search space m'=m. For the PDCCH UE specific search space, for the
serving cell on which PDCCH is monitored, if the monitoring UE is
configured with carrier indicator field then
m'=m+M.sup.(L)*n.sub.CI where n.sub.CI is the carrier indicator
field (CIF) value, else if the monitoring UE is not configured with
carrier indicator field then m'=m, where m=0, 1, . . . ,
M.sup.(L)-1. M.sup.(L) is the number of PDCCH candidates to monitor
at aggregation level L in the given search space. The carrier
indication field value can be the same as a serving cell index
(ServCellIndex). For the common search space, Y.sub.k is set to 0
for the two aggregation levels L=4 and L=8. For the UE-specific
search space S.sup.(L)k at aggregation level D, the variable
Y.sub.k is defined by "Y.sub.k=(AY.sub.k-1) mod D", where
Y.sub.-1=n.sub.RNTI.noteq.0, A=39827, D=65537 and
k=floor(n.sub.s/2). n.sub.s is the slot number within a radio
frame.
[0086] The eNB transmits an actual PDCCH (DCI) on a PDCCH candidate
in a search space and the UE monitors the search space to detect
the PDCCH (DCI). Here, monitoring implies attempting to decode each
PDCCH in the corresponding SS according to all monitored DCI
formats. The UE may detect a PDCCH thereof by monitoring a
plurality of PDCCHs. Basically, the UE does not know the location
at which a PDCCH thereof is transmitted. Therefore, the UE attempts
to decode all PDCCHs of the corresponding DCI format for each
subframe until a PDCCH having an ID thereof is detected and this
process is referred to as blind detection (or blind decoding
(BD)).
[0087] For example, it is assumed that a specific PDCCH is
CRC-masked with a radio network temporary identity (RNTI) `A` and
information about data transmitted using a radio resource `B` (e.g.
frequency location) and using transport format information `C`
(e.g. transmission block size, modulation scheme, coding
information, etc.) is transmitted in a specific DL subframe. Then,
the UE monitors the PDCCH using RNTI information thereof. The UE
having the RNTI `A` receives the PDCCH and receives the PDSCH
indicated by `B` and `C` through information of the received
PDCCH.
[0088] FIG. 4 illustrates the structure of a UL subframe used in a
wireless communication system.
[0089] Referring to FIG. 4, a UL subframe may be divided into a
data region and a control region in the frequency domain. One or
several PUCCHs may be allocated to the control region to deliver
UCI. One or several PUSCHs may be allocated to the data region of
the UE subframe to carry user data.
[0090] In the UL subframe, subcarriers distant from a direct
current (DC) subcarrier are used as the control region. In other
words, subcarriers located at both ends of a UL transmission BW are
allocated to transmit UCI. A DC subcarrier is a component unused
for signal transmission and is mapped to a carrier frequency
f.sub.0 in a frequency up-conversion process. A PUCCH for one UE is
allocated to an RB pair belonging to resources operating on one
carrier frequency and RBs belonging to the RB pair occupy different
subcarriers in two slots. The PUCCH allocated in this way is
expressed by frequency hopping of the RB pair allocated to the
PUCCH over a slot boundary. If frequency hopping is not applied,
the RB pair occupies the same subcarriers.
[0091] The PUCCH may be used to transmit the following control
information. [0092] Scheduling request (SR): SR is information used
to request a UL-SCH resource and is transmitted using an on-off
keying (OOK) scheme. [0093] HARQ-ACK: HARQ-ACK is a response to a
PDCCH and/or a response to a DL data packet (e.g. a codeword) on a
PDSCH. HARQ-ACK indicates whether the PDCCH or PDSCH has been
successfully received. 1-bit HARQ-ACK is transmitted in response to
a single DL codeword and 2-bit HARQ-ACK is transmitted in response
to two DL codewords. A HARQ-ACK response includes a positive ACK
(simply, ACK), negative ACK (NACK), discontinuous transmission
(DTX), or NACK/DRX. HARQ-ACK is used interchangeably with HARQ
ACK/NACK and ACK/NACK. [0094] Channel state information (CSI): CSI
is feedback information for a DL channel. CSI may include channel
quality information (CQI), a precoding matrix indicator (PMI), a
precoding type indicator, and/or a rank indicator (RI). In the CSI,
MIMO-related feedback information includes the RI and the PMI. The
RI indicates the number of streams or the number of layers that the
UE can receive through the same time-frequency resource. The PMI is
a value reflecting a space characteristic of a channel, indicating
an index of a preferred precoding matrix for DL signal transmission
based on a metric such as an SINR. The CQI is a value of channel
strength, indicating a received SINR that can be obtained by the UE
generally when the eNB uses the PMI.
[0095] A general wireless communication system performs data
transmission/reception through one downlink (DL) band and through
one uplink (UL) band corresponding to the DL band (in case of a
frequency division duplex (FDD) mode), or divides a prescribed
radio frame into a UL time unit and a DL time unit in the time
domain and then performs data transmission/reception through the
UL/DL time unit (in case of a time division duplex (TDD) mode).
Recently, to use a wider frequency band in recent wireless
communication systems, introduction of carrier aggregation (or BW
aggregation) technology that uses a wider UL/DL BW by aggregating a
plurality of UL/DL frequency blocks has been discussed. A carrier
aggregation (CA) is different from an orthogonal frequency division
multiplexing (OFDM) system in that DL or UL communication is
performed using a plurality of carrier frequencies, whereas the
OFDM system carries a base frequency band divided into a plurality
of orthogonal subcarriers on a single carrier frequency to perform
DL or UL communication. Hereinbelow, each of carriers aggregated by
carrier aggregation will be referred to as a component carrier
(CC).
[0096] For example, three 20 MHz CCs may be aggregated on each of a
UL and a DL to support a bandwidth of 60 MHz. The respective CCs
may be contiguous or non-contiguous in the frequency domain. For
convenience, although it has been described that the bandwidth of
UL CC and the bandwidth of DL CC are the same as each other and
symmetric to each other, the bandwidth of each CC may be
independently determined. Asymmetrical carrier aggregation in which
the number of UL CCs is different from the number of DL CCs may be
implemented. DL/UL CC limited to a specific UE may be referred to
as a serving UL/DL CC configured for the specific UE.
[0097] Meanwhile, the 3GPP LTE-A standard uses the concept of a
cell to manage radio resources. The "cell" associated with the
radio resources is defined by combination of downlink resources and
uplink resources, that is, combination of DL CC and UL CC. The cell
may be configured by downlink resources only, or may be configured
by downlink resources and uplink resources. If carrier aggregation
is supported, linkage between a carrier frequency of the downlink
resources (or DL CC) and a carrier frequency of the uplink
resources (or UL CC) may be indicated by system information. For
example, combination of the DL resources and the UL resources may
be indicated by linkage of system information block type 2 (SIB2).
In this case, the carrier frequency means a center frequency of
each cell or CC. A cell operating on a primary frequency may be
referred to as a primary cell (Pcell) or PCC, and a cell operating
on a secondary frequency may be referred to as a secondary cell
(Scell) or SCC. The carrier corresponding to the Pcell on downlink
will be referred to as a downlink primary CC (DL PCC), and the
carrier corresponding to the Pcell on uplink will be referred to as
an uplink primary CC (UL PCC). A Scell means a cell that may be
configured after completion of radio resource control (RRC)
connection establishment and used to provide additional radio
resources. The Scell may form a set of serving cells for the UE
together with the Pcell in accordance with capabilities of the UE.
The carrier corresponding to the Scell on the downlink will be
referred to as downlink secondary CC (DL SCC), and the carrier
corresponding to the Scell on the uplink will be referred to as
uplink secondary CC (UL SCC). Although the UE is in RRC-CONNECTED
state, if it is not configured by carrier aggregation or does not
support carrier aggregation, a single serving cell configured by
the Pcell only exists.
[0098] The eNB may activate all or some of the serving cells
configured in the UE or deactivate some of the serving cells for
communication with the UE. The eNB may change the
activated/deactivated cell, and may change the number of cells
which is/are activated or deactivated. If the eNB allocates
available cells to the UE cell-specifically or UE-specifically, at
least one of the allocated cells is not deactivated unless cell
allocation to the UE is fully reconfigured or unless the UE
performs handover. Such a cell which is not deactivated unless CC
allocation to the UE is fully reconfigured will be referred to as
Pcell, and a cell which may be activated/deactivated freely by the
eNB will be referred to as Scell. The Pcell and the Scell may be
discriminated from each other on the basis of the control
information. For example, specific control information may be set
to be transmitted and received through a specific cell only. This
specific cell may be referred to as the Pcell, and the other
cell(s) may be referred to as Scell(s).
[0099] A configured cell refers to a cell in which carrier
aggregation is performed for a UE based on measurement report from
another eNB or UE among cells of an eNB and is configured per UE.
The cell configured for the UE may be a serving cell in terms of
the UE. For the cell configured for the UE, i.e. the serving cell,
resources for ACK/NACK transmission for PDSCH transmission are
reserved in advance. An activated cell refers to a cell configured
to be actually used for PDSCH/PUSCH transmission among cells
configured for the UE and CSI reporting and SRS transmission for
PDSCH/PUSCH transmission are performed in the activated cell. A
deactivated cell refers to a cell configured not to be used for
PDSCH/PUSCH transmission by the command of an eNB or the operation
of a timer and, if a cell is deactivated, CSI reporting and SRS
transmission are also stopped in the cell.
[0100] For reference, a carrier indicator (CI) denotes a serving
cell index (ServCellIndex), CI=0 is applied to Pcell. The serving
cell index is a short ID used to identify a serving cell. For
example, any one of integers from 0 to `maximum number of carrier
frequencies which can be configured for the UE at a time-1` may be
allocated to one serving cell as the serving cell index. That is,
the serving cell index may be a logical index used to identify a
specific serving cell among cells allocated to the UE rather than a
physical index used to identify a specific carrier frequency among
all carrier frequencies.
[0101] As described above, the term "cell" used in carrier
aggregation is differentiated from the term "cell" indicating a
certain geographical area where a communication service is provided
by one eNB or one antenna group.
[0102] The cell mentioned in the present invention means a cell of
carrier aggregation which is combination of UL CC and DL CC unless
specifically noted.
[0103] Meanwhile, since one serving cell is only present in case of
communication based on a single carrier, a PDCCH carrying UL/DL
grant and corresponding PUSCH/PDSCH are transmitted on one cell. In
other words, in case of FDD under a single carrier environment, a
PDCCH for a DL grant for a PDSCH, which will be transmitted on a
specific DL CC, is transmitted on the specific CC, and a PDCCH for
a UL grant for a PUSCH, which will be transmitted on a specific UL
CC, is transmitted on a DL CC linked to the specific UL CC. In case
of TDD under a single carrier environment, a PDCCH for a DL grant
for a PDSCH, which will be transmitted on a specific DL CC, is
transmitted on the specific CC, and a PDCCH for a UL grant for a
PUSCH, which will be transmitted on a specific UL CC, is
transmitted on the specific CC.
[0104] In legacy systems subject to communication with one node,
the UE-RS, CSI-RS, and CRS are transmitted at the same location,
and therefore the UE does not consider a situation in which delay
spread, Doppler spread, frequency shift, average received power,
and received timing differ among the UE-RS port(s), CSI-RS port(s)
and CRS port(s0. However, for a communication system to which
coordinated Multi-Point (CoMP) communication technology allowing
more than one node to simultaneously participate in communication
with the UE is applied, the properties may differ among the PDCCH
port(s), PDSCH port(s), UE-RS port(s), CSI-RS port(s) and/or CRS
port(s). For this reason, the concept of a "quasi co-located
antenna port" is introduced for a mode (hereinafter, CoMP mode) in
which multiple nodes can participate in communication.
[0105] With respect to antenna ports, the term "Quasi co-located
(QCL)" or "quasi co-location (QCL)" can be defined as follows: if
two antenna ports are QCL, the UE may assume that the large-scale
properties of a signal received through one of the two antenna
ports can be inferred from the signal received through the other
antenna port. The large-scale properties include delay spread,
Doppler spread, frequency shift, average received power and/or
received timing.
[0106] With respect to channels, the term QCL may also be defined
as follows: if two antenna ports are QCL, the UE may assume that
the large-scale properties of a channel for conveying a symbol on
one of the two antenna ports can be inferred from the large-scale
properties of a channel for conveying a symbol on the other antenna
port. The large-scale properties include delay spread, Doppler
spread, Doppler shift, average gain and/or average delay.
[0107] One of the two definitions of QCL given above may be applied
to the embodiments of the present invention. Alternatively, the
definition of QCL may be modified to assume that antenna ports for
which QCL assumption is established are co-located. For example,
QCL may be defined in a manner that the UE assumes that the antenna
ports for which QCL assumption is established are antenna ports of
the same transmission point.
[0108] For non-quasi co-located (NQC) antenna ports, the UE cannot
assume the same large-scale properties between the antenna ports.
In this case, a typical UE needs to perform independent processing
for each NQC antenna with respect to timing acquisition and
tracking, frequency offset estimation and compensation, and delay
estimation and Doppler estimation.
[0109] On the other hand, for antenna ports for which QCL
assumption can be established, the UE performs the following
operations:
[0110] Regarding Doppler spread, the UE may apply the results of
estimation of the power-delay-profile, the delay spread and Doppler
spectrum and the Doppler spread for one port to a filter (e.g., a
Wiener filter) which is used for channel estimation for another
port;
[0111] Regarding frequency shift and received timing, after
performing time and frequency synchronization for one port, the UE
may apply the same synchronization to demodulation on another
port;
[0112] Further, regarding average received power, the UE may
average measurements of reference signal received power (RSRP) over
two or more antenna ports.
[0113] For example, if the UE receives a specific DMRS-based
DL-related DCI format (e.g., DCI format 2C) over a PDCCH/EPDCCH,
the UE performs data demodulation after performing channel
estimation of the PDSCH through a configured DMRS sequence. If the
UE can make an assumption that a DMRS port configuration received
through the DL scheduling grant and a port for a specific RS (e.g.,
a specific CSI-RS, a specific CRS, a DL serving cell CRS of the UE,
etc.) port are QCL, then the UE may apply the estimate(s) of the
large-scale properties estimated through the specific RS port to
channel estimation through the DMRS port, thereby improving
processing performance of the DMRS-based receiver.
[0114] FIG. 5 illustrates configuration of cell specific reference
signals (CRSs) and user specific reference signals (UE-RS). In
particular, FIG. 5 shows REs occupied by the CRS(s) and UE-RS(s) on
an RB pair of a subframe having a normal CP.
[0115] In an existing 3GPP system, since CRSs are used for both
demodulation and measurement, the CRSs are transmitted in all DL
subframes in a cell supporting PDSCH transmission and are
transmitted through all antenna ports configured at an eNB.
[0116] Referring to FIG. 5, the CRS is transmitted through antenna
ports p=0, p=0,1, p=0,1,2,3 in accordance with the number of
antenna ports of a transmission mode. The CRS is fixed to a certain
pattern within a subframe regardless of a control region and a data
region. The control channel is allocated to a resource of the
control region, to which the CRS is not allocated, and the data
channel is also allocated to a resource of the data region, to
which the CRS is not allocated.
[0117] A UE may measure CSI using the CRSs and demodulate a signal
received on a PDSCH in a subframe including the CRSs. That is, the
eNB transmits the CRSs at predetermined locations in each RB of all
RBs and the UE performs channel estimation based on the CRSs and
detects the PDSCH. For example, the UE may measure a signal
received on a CRS RE and detect a PDSCH signal from an RE to which
the PDSCH is mapped using the measured signal and using the ratio
of reception energy per CRS RE to reception energy per PDSCH mapped
RE. However, when the PDSCH is transmitted based on the CRSs, since
the eNB should transmit the CRSs in all RBs, unnecessary RS
overhead occurs. To solve such a problem, in a 3GPP LTE-A system, a
UE-specific RS (hereinafter, UE-RS) and a CSI-RS are further
defined in addition to a CRS. The UE-RS is used for demodulation
and the CSI-RS is used to derive CSI. The UE-RS is one type of DRS.
Since the UE-RS and the CRS are used for demodulation, the UE-RS
and the CRS may be regarded as demodulation RSs in terms of usage.
Since the CSI-RS and the CRS are used for channel measurement or
channel estimation, the CSI-RS and the CRS may be regarded as
measurement RSs.
[0118] Referring to FIG. 5, UE-RSs are transmitted on antenna
port(s) p=5, p=7, p=8 orp=7, 8, . . . , .nu.+6 for PDSCH
transmission, where .nu. is the number of layers used for the PDSCH
transmission. UE-RSs are present and are a valid reference for
PDSCH demodulation only if the PDSCH transmission is associated
with the corresponding antenna port. UE-RSs are transmitted only on
RBs to which the corresponding PDSCH is mapped. That is, the UE-RSs
are configured to be transmitted only on RB(s) to which a PDSCH is
mapped in a subframe in which the PDSCH is scheduled unlike CRSs
configured to be transmitted in every subframe irrespective of
whether the PDSCH is present. Accordingly, overhead of the RS may
be lowered compared to that of the CRS.
[0119] In the 3GPP LTE-A system, the UE-RSs are defined in a PRB
pair. Referring to FIG. 5, in a PRB having frequency-domain index
n.sub.PRB assigned for PDSCH transmission with respect to p=7, p=8,
or p=7, 8, . . . , .nu.+6, a part of UE-RS sequence r(m) is mapped
to complex-valued modulation symbols a.sup.(p).sub.k,l in a
subframe according to the following equation.
a.sub.k,l.sup.(p)=w.sub.p(l')r(3l'N.sub.RB.sup.max,DL+3n.sub.PRB+m')
EQUATION 1
where w.sub.p(i), l', m' are given as follows.
w p ( i ) = { w _ p ( i ) ( m ' + n PRB ) mod 2 = 0 w _ p ( 3 - i )
( m ' + n PRB ) mod 2 = 1 k = 5 m ' + N sc RB n PRB + k ' k ' = { 1
p .di-elect cons. { 7 , 8 , 11 , 13 } 0 p .di-elect cons. { 9 , 10
, 12 , 14 } l = { l ' mod 2 + 2 if in a special subframe with
configuration 3 , 4 , 8 or 9 ( see Table 2 ) l ' mod 2 + 2 + 3 l '
/ 2 if in a special subframe with configuration 1 , 2 , 6 , or 7 (
see Table 2 ) l ' mod 2 + 5 if not in a special subframe l ' = { 0
, 1 , 2 , 3 if n s mod 2 = 0 and in a special subframe with
configuration 1 , 2 , 6 , or 7 ( see Table 2 ) 0 , 1 if n s mod 2 =
0 and not in special subframe with configuration 1 , 2 , 6 , or 7 (
see Table 2 ) 2 , 3 if n s mod 2 = 1 and not in special subframe
with configuration 1 , 2 , 6 , or 7 ( see Table 2 ) m ' = 0 , 1 , 2
EQUATION 2 ##EQU00001##
where n.sub.s is the slot number within a radio frame and an
integer among 0 to 19. The sequence w.sub.p (i) for normal CP is
given according to the following equation.
TABLE-US-00008 TABLE 8 Antenna port p [w.sub.p (0) w.sub.p (1)
w.sub.p (2) w.sub.p (3)] 7 [+1 +1 +1 +1] 8 [+1 -1 +1 -1] 9 [+1 +1
+1 +1] 10 [+1 -1 +1 -1] 11 [+1 +1 -1 -1] 12 [-1 -1 +1 +1] 13 [+1 -1
-1 +1] 14 [-1 +1 +1 -1]
[0120] For antenna port p.di-elect cons.{7, 8, . . . , .nu.+6}, the
UE-RS sequence r(m) is defined as follows.
r ( m ) = 1 2 ( 1 - 2 c ( 2 m ) ) + j 1 2 ( 1 - 2 c ( 2 m + 1 ) ) ,
m = { 0 , 1 , , 12 N RB max , DL - 1 normal cyclic prefix 0 , 1 , ,
16 N RB max , DL - 1 extended cyclic prefix EQUATION 3
##EQU00002##
where c(i) is a pseudo-random sequence defined by a length-31 Gold
sequence. The output sequence c(n) of length M.sub.PN, where n=0,
1, . . . , M.sub.PN-1, is defined by the following equation.
c(n)=(x.sub.1(n+N.sub.C)+x.sub.2(n+N.sub.C))mod 2
x.sub.1(n+31)=(x.sub.1(n+3)+x.sub.1(n))mod 2
x.sub.2(n+31)=(x.sub.2(n+3)+x.sub.2(n+2)+x.sub.2(n+1)+x.sub.2(n))mod
2 EQUATION 4
where N.sub.C=1600 and the first m-sequence is initialized with
x.sub.1(0)=1, x.sub.1(n)=0, n=1, 2, . . . ,30. The initialization
of the second m-sequence is denoted by
c.sub.init=.SIGMA..sub.i=0.sup.30x.sub.2(i)2.sup.i with the value
depending on the application of the sequence.
[0121] In EQUATION 3, the pseudo-random sequence generator for
generating c(i) is initialized with c.sub.init at the start of each
subframe according to the following equation.
c.sub.init=(.left brkt-bot.n.sub.s/2.right
brkt-bot.+1)(2n.sub.ID.sup.(n.sup.SCID.sup.)+1)2.sup.16+n.sub.SCID
EQUATION 5
[0122] where the quantities n.sup.(i).sub.ID, i=0,1, which is
corresponding to n.sup.(nSCID).sub.ID, are given by a physical
layer cell identity N.sup.cell.sub.ID if no value for a scrambling
identity n.sup.DMRS,i.sub.ID is provided by higher layers or if DCI
format 1A, 2B or 2C is used for DCI format associated with the
PDSCH transmission, and given by n.sup.DMRS,i.sub.ID otherwise.
[0123] In EQUATION 5, the value of n.sub.SCID is zero unless
specified otherwise. For a PDSCH transmission on antenna ports 7 or
8, n.sub.SCID is given by the DCI format 2B or 2C. DCI format 2B is
a DCI format for resource assignment for a PDSCH using a maximum of
two antenna ports having UE-RSs. DCI format 2C is a DCI format for
resource assignment for a PDSCH using a maximum of 8 antenna ports
having UE-RSs
[0124] Meanwhile, if RRH technology, cross-carrier scheduling
technology, etc. are introduced, the amount of PDCCH which should
be transmitted by the eNB is gradually increased. However, since a
size of a control region within which the PDCCH may be transmitted
is the same as before, PDCCH transmission acts as a bottleneck of
system throughput. Although channel quality may be improved by the
introduction of the aforementioned multi-node system, application
of various communication schemes, etc., the introduction of a new
control channel is required to apply the legacy communication
scheme and the carrier aggregation technology to a multi-node
environment. Due to the need, a configuration of a new control
channel in a data region (hereinafter, referred to as PDSCH region)
not the legacy control region (hereinafter, referred to as PDCCH
region) has been discussed. Hereinafter, the new control channel
will be referred to as an enhanced PDCCH (hereinafter, referred to
as EPDCCH)
[0125] FIG. 6 is a example of a downlink control channel configured
in a data region of a DL subframe.
[0126] The EPDCCH may be configured within rear OFDM symbols
starting from a configured OFDM symbol, instead of front OFDM
symbols of a subframe. The EPDCCH may be configured using
continuous frequency resources, or may be configured using
discontinuous frequency resources for frequency diversity. By using
the EPDCCH, control information per node may be transmitted to a
UE, and a problem that a legacy PDCCH region may not be sufficient
may be solved. For reference, the PDCCH may be transmitted through
the same antenna port(s) as that(those) configured for transmission
of a CRS, and a UE configured to decode the PDCCH may demodulate or
decode the PDCCH by using the CRS. Unlike the PDCCH transmitted
based on the CRS, the EPDCCH is transmitted based on the
demodulation RS (hereinafter, DMRS). Accordingly, the UE
decodes/demodulates the PDCCH based on the CRS and
decodes/demodulates the EPDCCH based on the DMRS. The DMRS
associated with EPDCCH is transmitted on the same antenna port
p.di-elect cons.{107,108,109,110} as the associated EPDCCH physical
resource, is present for EPDCCH demodulation only if the EPDCCH
transmission is associated with the corresponding antenna port, and
is transmitted only on the PRB(s) upon which the corresponding
EPDCCH is mapped. For example, the REs occupied by the UE-RS(s) of
the antenna port 7 or 8 may be occupied by the DMRS(s) of the
antenna port 107 or 108 on the PRB to which the EPDCCH is mapped,
and the REs occupied by the UE-RS(s) of antenna port 9 or 10 may be
occupied by the DMRS(s) of the antenna port 109 or 110 on the PRB
to which the EPDCCH is mapped. In other words, a certain number of
REs are used on each RB pair for transmission of the DMRS for
demodulation of the EPDCCH regardless of the UE or cell if the type
of EPDCCH and the number of layers are the same as in the case of
the UE-RS for demodulation of the PDSCH.
[0127] For each serving cell, higher layer signaling can configure
a UE with one or two EPDCCH-PRB-sets for EPDCCH monitoring. The
PRB-pairs corresponding to an EPDCCH-PRB-set are indicated by
higher layers. Each EPDCCH-PRB-set consists of set of ECCEs
numbered from 0 to N.sub.ECCE,p,k-1, where N.sub.ECCE,p,k is the
number of ECCEs in EPDCCH-PRB-set p of subframe k. Each
EPDCCH-PRB-set can be configured for either localized EPDCCH
transmission or distributed EPDCCH transmission.
[0128] The UE shall monitor a set of EPDCCH candidates on one or
more activated serving cells as configured by higher layer
signaling for control information.
[0129] The set of EPDCCH candidates to monitor are defined in terms
of EPDCCH UE-specific search spaces. For each serving cell, the
subframes in which the UE monitors EPDCCH UE-specific search spaces
are configured by higher layers.
[0130] An EPDCCH UE-specific search space ES.sup.(L).sub.k at
aggregation level L.di-elect cons.{1,2,4,8,16,32} is defined by a
set of EPDCCH candidates.
[0131] For an EPDCCH-PRB-set p, the ECCEs corresponding to EPDCCH
candidate m of the search space ES.sup.(L)k are given by the
following equation.
L { ( Y p , k + m E ECCE , p , k L M p ( L ) + b ) mod N ECCE , p ,
k / L } + i Equation 6 ##EQU00003##
where i=0, . . . , L-1. b=n.sub.CI if the UE is configured with a
carrier indicator field for the serving cell on which EPDCCH is
monitored, otherwise b=0. n.sub.CI is the carrier indicator field
(CIF) value, which is the same as a serving cell index
(ServCellIndex). m=0, 1, . . . , M.sup.(L).sub.p-1, M.sup.(L).sub.p
is the number of EPDCCH candidates to monitor at aggregation level
L in EPDDCH-PRB-set p. The variable Y.sub.p,k is defined by
`Y.sub.p,k=(A.sub.pY.sub.p,k-1) mod D`, where
Y.sub.p,k-1=n.sub.RNTI.noteq.0, A.sub.0=39827,
A.sub.0=39829,D=65537 and k=floor(n.sub.s/2). n.sub.s is the slot
number within a radio frame.
[0132] A UE is not expected to monitor an EPDCCH candidate, if an
ECCE corresponding to that EPDCCH candidate is mapped to a PRB pair
that overlaps in frequency with a transmission of either PBCH or
PSS/SSS in the same subframe.
[0133] An EPDCCH is transmitted using an aggregation of one or
several consecutive enhanced control channel elements (ECCEs). Each
ECCE consists of multiple enhanced resource element groups (EREGs).
EREGs are used for defining the mapping of enhanced control
channels to resource elements. There are 16 EREGs, numbered from 0
to 15, per physical resource block (PRB) pair. Number all resource
elements (REs), except resource elements carrying DMRS
(hereinafter, EPDCCH DMRS) for demodulation of the EPDCCH, in a
physical resource-block pair cyclically from 0 to 15 in an
increasing order of first frequency. Therefore, all the REs, except
REs carrying the EPDCCH DMRS, in the PRB pair has any one of
numbers 0 to 15. All REs with number i in that PRB pair constitutes
EREG number i. As described above, it is noted that EREGs are
distributed on frequency and time axes within the PRB pair and an
EPDCCH transmitted using aggregation of one or more ECCEs, each of
which includes a plurality of EREGs, is also distributed on
frequency and time axes within the PRB pair.
[0134] The number of ECCEs used for one EPDCCH depends on the
EPDCCH format as given by TABLE 9, the number of EREGs per ECCE is
given by TABLE 10. TABLE 9 shows an example of supported EPDCCH
formats, and TABLE 10 shows an example of the number of EREGs per
ECCE, N.sup.EREG.sub.ECCE. Both localized and distributed
transmission is supported.
TABLE-US-00009 TABLE 9 Number of ECCEs for one EPDCCH,
N.sub.ECCE.sup.EPDCCH Case A Case B EPDCCH Localized Distributed
Localized Distributed format transmission transmission transmission
transmission 0 2 2 1 1 1 4 4 2 2 2 8 8 4 4 3 16 16 8 8 4 -- 32 --
16
TABLE-US-00010 TABLE 10 Normal cyclic prefix Extended cyclic prefix
Special Special subframe, subframe, Normal Special subframe,
configuration Normal configuration subframe configuration 3, 4, 8
1, 2, 6, 7, 9 subframe 1, 2, 3, 5, 6 4 8
[0135] An EPDCCH can use either localized or distributed
transmission, differing in the mapping of ECCEs to EREGs and PRB
pairs. One or two sets of PRB pairs which a UE shall monitor for
EPDCCH transmissions can be configured. All EPDCCH candidates in
EPDCCH set S.sub.p (i.e., EPDCCH-PRB-set) use either only localized
or only distributed transmission as configured by higher layers.
Within EPDCCH set S.sub.p in subframe k, the ECCEs available for
transmission of EPDCCHs are numbered from 0 to N.sub.ECCE,p,k-1.
ECCE number n is corresponding to the following EREG(s): [0136]
EREGs numbered (n mod N.sup.ECCE.sub.RB)+jN.sup.ECCE.sub.RB in PRB
index floor(n/N.sup.ECCE.sub.RB) for localized mapping, and [0137]
EREGs numbered floor (n/N.sup.Sm.sub.RB)+jN.sup.ECCE.sub.RB in PRB
indices (n+jmax(1,N.sup.Sp.sub.RBN.sup.EREG.sub.ECCE))mod
N.sup.Sp.sub.RB for distributed mapping,
[0138] where j=0, 1, . . . , N.sup.EREG.sub.ECCE-1,
N.sup.EREG.sub.ECCE is the number of EREGs per ECCE, and
N.sup.ECCE.sub.RB=16/N.sup.EREG.sub.ECCE is the number of ECCEs per
RB pair. The PRB pairs constituting EPDCCH set S.sub.p are assumed
to be numbered in ascending order from 0 to N.sup.Sp.sub.RB-1.
[0139] Case A in TABLE 9 applies when: [0140] DCI formats 2, 2A,
2B, 2C or 2D is used and N.sup.DL.sub.RB>25, or [0141] any DCI
format when n.sub.EPDCCH<104 and normal cyclic prefix is used in
normal subframes or special subframes with configuration 3, 4,
8.
[0142] Otherwise case 2 is used. The quantity n.sub.EPDCCH for a
particular UE is defined as the number of downlink resource
elements (k,l) in a PRB pair configured for possible EPDCCH
transmission of EPDCCH set S.sub.0 and and fulfilling all of the
following criteria, [0143] they are part of any one of the 16 EREGs
in the physical resource-block pair, [0144] they are assumed by the
UE not to be used for CRSs or CSI-RSs, [0145] the index l in a
subframe fulfils l.gtoreq.l.sub.EPDCCHStart.
[0146] where l.sub.EPDCCHStart is given based on higher layer
signaling `epdcch-StartSymbol-r11`, higher layer signaling
`pdsch-Start-r11`, or CFI value carried by PCFICH.
[0147] The mapping to resource elements (k,l) on antenna port p
meeting the criteria above is in increasing order of first the
index k and then the index l, starting with the first slot and
ending with the second slot in a subframe.
[0148] For localized transmission, the single antenna port p to use
is given by TABLE 11 with n'=n.sub.ECCE,low mod
N.sup.ECCE.sub.RB+n.sub.RNTI mod
min(N.sup.ECCE.sub.EPDCCH,N.sup.ECCE.sub.RB), where n.sub.ECCE,low
is the lowest ECCE index used by this EPDCCH transmission in the
EPDCCH set, n.sub.RNTI corresponds to the RNTI associated with the
EPDCCH transmission, and N.sup.ECCE.sub.EPDCCH is the number of
ECCEs used for this EPDCCH.
TABLE-US-00011 TABLE 11 Normal cyclic prefix Normal subframes,
Extended Special subframes, Special subframes, cyclic prefix n'
configurations 3, 4, 8 configurations 1, 2, 6, 7, 9 Any subframe 0
107 107 107 1 108 109 108 2 109 -- -- 3 110 -- --
[0149] For distributed transmission, each resource element in an
EREG is associated with one out of two antenna ports in an
alternating manner where p.di-elect cons.{107,109} for normal
cyclic prefix and p.di-elect cons.{107,108} for extended cyclic
prefix
[0150] Recently, machine type communication (MTC) has come to the
fore as a significant communication standard issue. MTC refers to
exchange of information between a machine and an eNB without
involving persons or with minimal human intervention. For example,
MTC may be used for data communication for
measurement/sensing/reporting such as meter reading, water level
measurement, use of a surveillance camera, inventory reporting of a
vending machine, etc. and may also be used for automatic
application or firmware update processes for a plurality of UEs. In
MTC, the amount of transmission data is small and UL/DL data
transmission or reception (hereinafter, transmission/reception)
occurs occasionally. In consideration of such properties of MTC, it
would be better in terms of efficiency to reduce production cost
and battery consumption of UEs for MTC (hereinafter, MTC UEs)
according to data transmission rate. Since the MTC UE has low
mobility, the channel environment thereof remains substantially the
same. If an MTC UE is used for metering, reading of a meter,
surveillance, and the like, the MTC UE is very likely to be located
in a place such as a basement, a warehouse, and mountain regions
which the coverage of a typical eNB does not reach. In
consideration of the purposes of the MTC UE, it is better for a
signal for the MTC UE to have wider coverage than the signal for
the conventional UE (hereinafter, a legacy UE).
[0151] When considering the usage of the MTC UE, there is a high
probability that the MTC UE requires a signal of wide coverage
compared with the legacy UE. Therefore, if the eNB transmits a
PDCCH, a PDSCH, etc. to the MTC UE using the same scheme as a
scheme of transmitting the PDCCH, the PDSCH, etc. to the legacy UE,
the MTC UE has difficulty in receiving the PDCCH, the PDSCH, etc.
Therefore, the present invention proposes that the eNB apply a
coverage enhancement scheme such as subframe repetition (repetition
of a subframe with a signal) or subframe bundling upon transmission
of a signal to the MTC UE having a coverage issue so that the MTC
UE can effectively receive a signal transmitted by the eNB. For
example, the PDCCH and PDSCH may be transmitted to the MTC UE
having the coverage issue in a plurality of subframes (e.g. about
100 subframes).
[0152] As one method of reducing the cost of an MTC UE, the MTC UE
may operate in, for example, a reduced DL and UL bandwidths of 1.4
MHz regardless of the system bandwidth when the cell operates. In
this case, a sub-band (i.e., narrowband) in which the MTC UE
operates may always be positioned at the center of a cell (e.g., 6
center PRBs) as shown in FIG. 6 (a), or multiple sub-bands for MTC
may be provided in one subframe to multiplex MTC UEs in the
subframe such that the UEs use different sub-bands or use the same
sub-band which is not a sub-band consisting of the 6 center
PRBs.
[0153] In this case, the MTC UE may not normally receive a legacy
PDCCH transmitted through the entire system bandwidth, and
therefore it may not be preferable to transmit a PDCCH for the MTC
UE in an OFDM symbol region in which the legacy PDCCH is
transmitted, due to an issue of multiplexing with a PDCCH
transmitted for another UE. As one method to address this issue,
introduction of a control channel transmitted in a sub-band in
which MTC operates for the MTC UE is needed. As a DL control
channel for such low-complexity MTC UE, a legacy EPDCCH may be
used. Alternatively, an M-PDCCH, which is a variant of the legacy
PDCCH/EPDCCH, may be introduced for the MTC UE.
[0154] A data channel (e.g., PDSCH, PUSCH) and/or control channel
(e.g., M-PDCCH, PUCCH, PHICH) may be transmitted across multiple
subframes to implement coverage enhancement (CE) of the UE, using a
repetition technique or TTI bundling technique. On behalf of the
CE, a control/data channel may be transmitted additionally using
techniques such as cross-subframe channel estimation and frequency
(narrowband) hopping. Herein, the cross-subframe channel estimation
refers to a channel estimation technique using not only a reference
signal in a subframe having a corresponding channel but also a
reference signal in neighboring subframe(s).
[0155] The MTC UE may need CE up to, for example, 15 dB. However,
not all MTC UEs are present in an environment which requires CE. In
addition, the QoS requirements for MTC UEs are not identical. For
example, devices such as a sensor and a meter have a low mobility
and a small amount of data to transmit/receive and are very likely
to be positioned in a shaded area. Accordingly, such devices may
need high CE. On the other hand, wearable devices such as a smart
watch may have mobility and are very likely to have a relatively
large amount of data to transmit/receive and to be positioned in a
place other than the shaded area. Accordingly, not all MTC UEs need
a high level of CE, and the required capability may depend on the
type of an MTC UE.
[0156] According to LTE-A Rel-13, CE may be divided into two modes.
In a first mode (referred to as CE mode A), transmission may not be
repeated or may be repeated only a few times. In a second mode (or
CE mode B), many repetitions of transmission are allowed. A mode to
enter between the two modes may be signaled to the MTC UE. Herein,
parameters that a low-complexity/low-cost UE assumes for
transmission/reception of a control channel/data channel may depend
on the CE mode. In addition, the DCI format which the
low-complexity/low-cost UE monitors may depend on the CE mode.
Transmission of some physical channels may be repeated the same
number of times regardless of whether the CE mode is CE mode A or
CE mode B.
[0157] Embodiments of the present invention described below are
applicable not only to the 3GPP LTE/LTE-A system but also to a
radio access technology (RAT) system. As many communication devices
increasingly require a higher communication capacity, a need for
mobile broadband communication improved over the legacy RAT has
been raised. Massive MTC providing various services anywhere by
connecting multiple devices and objects is one of the main issues
which will be considered for future communication. Additionally,
design of a communication system in consideration of a service/UE
sensitive to reliability and latency is under discussion. As such,
introduction of future generation RAT in consideration of advanced
mobile broadband communication, massive MTC and ultra-reliable and
low latency communication (URLLC) is under discussion. For
simplicity, this technology will be referred to as a new RAT in
this specification.
[0158] In the next system of LTE-A, a method of reducing the
latency of data transmission is considered. Packet data latency is
one of the performance metrics that vendors, operators and also
end-users (via speed test applications) regularly measure. Latency
measurements are done in all phases of a radio access network
system lifetime, when verifying a new software release or system
component, when deploying a system and when the system is in
commercial operation.
[0159] Better latency than previous generations of 3GPP RATs was
one performance metric that guided the design of LTE. LTE is also
now recognized by the end-users to be a system that provides faster
access to internet and lower data latencies than previous
generations of mobile radio technologies.
[0160] However, with respect to further improvements specifically
targeting the delays in the system little has been done. Packet
data latency is important not only for the perceived responsiveness
of the system; it is also a parameter that indirectly influences
the throughput. HTTP/TCP is the dominating application and
transport layer protocol suite used on the internet today.
According to HTTP Archive (http://httparchive.org/trends.php) the
typical size of HTTP-based transactions over the internet are in
the range from a few 10's of Kbytes up to 1 Mbyte. In this size
range, the TCP slow start period is a significant part of the total
transport period of the packet stream. During TCP slow start the
performance is latency limited. Hence, improved latency can rather
easily be shown to improve the average throughput, for this type of
TCP-based data transactions. In addition, to achieve really high
bit rates (in the range of Gbps), UE L2 buffers need to be
dimensioned correspondingly. The longer the round trip time (RTT)
is, the bigger the buffers need to be. The only way to reduce
buffering requirements in the UE and eNB side is to reduce
latency.
[0161] Radio resource efficiency could also be positively impacted
by latency reductions. Lower packet data latency could increase the
number of transmission attempts possible within a certain delay
bound; hence higher block error ration (BLER) targets could be used
for the data transmissions, freeing up radio resources but still
keeping the same level of robustness for users in poor radio
conditions. The increased number of possible transmissions within a
certain delay bound, could also translate into more robust
transmissions of real-time data streams (e.g. VoLTE), if keeping
the same BLER target. This would improve the VoLTE voice system
capacity.
[0162] There are more over a number of existing applications that
would be positively impacted by reduced latency in terms of
increased perceived quality of experience: examples are gaming,
real-time applications like VoLTE/OTT VoIP and video
telephony/conferencing.
[0163] Going into the future, there will be a number of new
applications that will be more and more delay critical. Examples
include remote control/driving of vehicles, augmented reality
applications in e.g. smart glasses, or specific machine
communications requiring low latency as well as critical
communications.
[0164] In embodiments of the present invention described below, the
term "assume" may mean that a subject to transmit a channel
transmits the channel in accordance with the corresponding
"assumption." This may also mean that a subject to receive the
channel receives or decodes the channel in a form conforming to the
"assumption," on the assumption that the channel has been
transmitted according to the "assumption."
[0165] FIG. 7 illustrates the length of a transmission time
interval (TTI) which is needed to implement low latency.
[0166] Referring to FIG. 7, a propagation delay (PD), a buffering
time, a decoding time, an A/N preparation time, an uplink PD, and
an OTA (over the air) delay according to a retransmission margin
are produced while a signal transmitted from the eNB reaches the
UE, the UE transmits an A/N for the signal, and the A/N reaches the
eNB. To satisfy low latency, a shortened TTI (sTTI) shorter than or
equal to 0.5 ms needs to be designed by shortening the TTI, which
is the smallest unit of data transmission. For example, to shorten
the OTA delay, which is a time taken from the moment the eNB starts
to transmit data (PDCCH and PDSCH) until the UE completes
transmission of an A/N for the data to the eNB, to a time shorter
than 1 ms, the TTI is preferably set to 0.21 ms. That is, to
shorten the user plane (U-plane) delay to 1 ms, the sTTI may be set
in the unit of about three OFDM symbols.
[0167] While FIG. 7 illustrates that the sTTI is configured with
three OFDM symbols to satisfy 1 ms as the OTA delay or U-plane
delay, an sTTI shorter than 1 ms may also be configured. For
example, for the normal CP, an sTTI consisting of 2 OFDM symbols,
an sTTI consisting of 4 OFDM symbols and/or an sTTI consisting of 7
OFDM symbols may be configured.
[0168] In the time domain, all OFDM symbols constituting a default
TTI or the OFDM symbols except the OFDM symbols occupying the PDCCH
region of the TTI may be divided into two or more sTTIs on some or
all frequency resources in the frequency band of the default TTI,
namely the channel band or system band of the TTI.
[0169] In the following description, a default TTI or main TTI used
in the system is referred to as a TTI or subframe, and the TTI
having a shorter length than the default/main TTI of the system is
referred to as an sTTI. For example, in a system in which a TTI of
1 ms is used as the default TTI as in the current LTE/LTE-A system,
a TTI shorter than 1 ms may be referred to as the sTTI. In
addition, in the following description, a physical downlink control
channel/physical downlink data channel/physical uplink control
channel/physical uplink data channel transmitted in units of the
default/main TTI are referred to as a PDCCH/PDSCH/PUCCH/PUSCH, and
a PDCCH/PDSCH/PUCCH/PUSCH transmitted within an sTTI or in units of
sTTI are referred to as sPDCCH/sPDSCH/sPUCCH/sPUSCH. In the new RAT
environment, the numerology may be changed, and thus a default/main
TTI different from that for the current LTE/LTE-A system may be
used. However, for simplicity, the default/main TTI will be
referred to as a TTI, subframe, legacy TTI or legacy subframe, and
a TTI shorter than 1 ms will be referred to as an sTTI, on the
assumption that the time length of the default/main TTI is 1 ms.
The method of transmitting/receiving a signal in a TTI and an sTTI
according to embodiments described below is applicable not only to
the system according to the current LTE/LTE-A numerology but also
to the default/main TTI and sTTI of the system according to the
numerology for the new RAT environment.
[0170] FIG. 8 illustrates an sTTI and transmission of a control
channel and data channel within the sTTI.
[0171] In the downlink environment, a PDCCH for
transmission/scheduling of data within an sTTI (i.e., sPDCCH) and a
PDSCH transmitted within an sTTI (i.e., sPDSCH) may be transmitted.
For example, referring to FIG. 8, a plurality of the sTTIs may be
configured within one subframe, using different OFDM symbols. For
example, the OFDM symbols in the subframe may be divided into one
or more sTTIs in the time domain. OFDM symbols constituting an sTTI
may be configured, excluding the leading OFDM symbols on which the
legacy control channel is transmitted. Transmission of the sPDCCH
and sPDSCH may be performed in a TDM manner within the sTTI, using
different OFDM symbol regions. In an sTTI, the sPDCCH and sPDSCH
may be transmitted in an FDM manner, using different regions of
PRB(s)/frequency resources.
[0172] The present invention is directed to a method of providing a
plurality of different services in one system by applying different
system parameters according to the services or UEs to satisfy the
requirements for the services. In particular, for a service/UE
sensitive to latency, an sTTI may be used to send data in a short
time and to allow a response to the data to be sent in a short
time. Thereby, the latency may be reduced as much as possible. On
the other hand, for a service/UE which is less sensitive to
latency, a longer TTI may be used to transmit/receive data. For a
service/UE which is sensitive to power efficiency rather than to
latency, data may be repeatedly transmitted at the same low power
or may be transmitted in units of a longer TTI. The present
invention proposes a transmission method and multiplexing method
for controlling information and data signals to enable the
operations described above. The proposed methods are associated
with the transmission aspect of a network, the reception aspect of
a UE, multiplexing of multiple TTIs in one UE, and multiplexing of
multiple TTIs between multiple UEs.
[0173] In contrast with the legacy LTE/LTE-A system, in which the
length of a TTI is fixed to 1 ms, and thus all UEs and eNB perform
signal transmission and reception in units of 1 ms, the present
invention supports a system which has multiple TTI lengths, and one
UE and one eNB may transmit and receive a signal using multiple TTI
lengths. In particular, the present invention proposes a method of
enabling the eNB and UE to communicate with each other while
supporting various TTI lengths and variability when the TTI length
is variable and a method of performing multiplexing for each
channel and UE. While description of the present invention below is
based on the legacy LTE-/LTE-A system, it is also applicable to
systems other than the LTE/LTE-A system or RAT.
[0174] FIG. 9 illustrates an example of short TTIs configured in a
legacy subframe.
[0175] In legacy LTE/LTE-A, if a subframe of 1 ms has a normal CP,
the subframe consists of 14 OFDM symbols. If a TTI shorter than 1
ms is configured, a plurality of TTIs may be configured within one
subframe. As shown in FIG. 9, each TTI may consist of, for example,
2 symbols, 3 symbols, 4 symbols, or 7 symbols. Although not shown
in FIG. 9, a TTI consisting of one symbol may also be considered.
If one symbol is one TTI unit, 12 TTIs may be configured in the
default TTI of 1 ms, on the assumption that the legacy PDCCH is
transmittable within two OFDM symbols. Similarly, when the two
leading OFDM symbols are assumed to be the legacy PDCCH region, and
two symbols are taken as one TTI unit, 6 TTIs may be configured
within the default TTI. If three symbols are taken as one TTI, 4
TTIs may be configured within the default TTI. If 4 symbols are
taken as one TTI unit, 3 TTIs may be configured within the default
TTI.
[0176] If the 7 symbols are configured as one TTI, a TTI consisting
of 7 leading symbols including the legacy PDCCH region and a TTI
consisting of 7 subsequent symbols may be configured. In this case,
if one TTI consists of 7 symbols, a UE supporting the short TTI
assumes that the two leading OFDM symbols on which the legacy PDCCH
is transmitted are punctured or rate-matched and the data and/or
control signals of the UE are transmitted on the five subsequent
symbols in the TTI (i.e., the TTI of the first slot) positioned at
the leading part of one subframe (i.e., default TTI). On the other
hand, the UE may assume that the data and/or control signals can be
transmitted on all 7 symbols in a TTI positioned at the rear part
of the same subframe (i.e., the TTI of the second slot) without any
rate-matched or punctured resource region.
[0177] Puncturing a channel on a specific resource means that the
signal of the channel is mapped to the specific resource in the
procedure of resource mapping of the channel, but a portion of the
signal mapped to the punctured resource is excluded in transmitting
the channel. In other words, the specific resource which is
punctured is counted as a resource for the channel in the procedure
of resource mapping of the channel, a signal mapped to the specific
resource among the signals of the channel is not actually
transmitted. The receiver of the channel receives, demodulates or
decodes the channel, assuming that the signal mapped to the
specific resource is not transmitted. On the other hand,
rate-matching of a channel on a specific resource means that the
channel is never mapped to the specific resource in the procedure
of resource mapping of the channel, and thus the specific resource
is not used for transmission of the channel. In other words, the
rate-matched resource is not counted as a resource for the channel
in the procedure of resource mapping of the channel. The receiver
of the channel receives, demodulates, or decodes the channel,
assuming that the specific rate-matched resource is not used for
mapping and transmission of the channel.
[0178] FIG. 10 illustrates another example of short TTIs (sTTIs)
configured in a legacy subframe
[0179] While FIG. 9 illustrates that the sTTIs configured in one
subframe have the same length, sTTIs having different lengths may
be configured in one subframe. For example, as shown in FIG. 10, an
sTTI consisting of 4 OFDM symbols and an sTTI consisting of 3 OFDM
symbols may coexist within one subframe.
[0180] This embodiment of the present invention suggests a
reference signal (RS) and a pattern of the RS (i.e., RS RE
location) which are used to demodulate a downlink physical control
channel (e.g., sPDCCH) and a data channel (e.g., sPDSCH) when the
downlink physical control channel and the data channel are
transmitted within a short TTI (hereinafter, sTTI).
[0181] A. RS Usage 1: Utilize Legacy CRS Only
[0182] An RS for demodulation of the sPDCCH and/or sPDSCH in an
sTTI may be identical to the legacy CRS. Accordingly, the UE may
use the legacy CRS to demodulate the sPDCCH and/or sPDSCH. In this
case, in order to demodulate a control/data channel transmitted
within a specific sTTI, a CRS transmitted in another sTTI may be
used (together) to perform channel estimation. Accordingly, the
achieved channel estimation performance may be higher than when
only the RS transmitted in the sTTI is used to perform channel
estimation. In addition, RS overhead may be minimized as the need
for transmission of an RS other than the conventional CRS is
eliminated.
[0183] In this case, since the legacy CRS is not transmitted in the
MBSFN subframe, UE may assume that the sTTI-based the sPDCCH/sPDSCH
is not transmitted in the MBSFN subframe. For example, the UE may
not expect reception of an sPDCCH/sPDSCH in the MBSFN subframe.
Alternatively, in order to support the sTTI in the MBSFN subframe,
an RS conforming to the legacy CRS sequence and pattern may be
transmitted in 1) the entire region of PRB(s) (in the corresponding
channel band), 2) in a region of (fixed or higher-layer signaled)
PRB(s) in which the sTTI-based operation is performed, or 3) in a
region of PRB(s) in which the sPDCCH and/or sPDSCH is
transmitted.
[0184] B. RS Usage 2: Additional RS Only
[0185] The RS for demodulation of the sPDCCH and/or sPDSCH in an
sTTI may be a new RS rather than the legacy CRS. Since such RS is
additionally transmitted along with the legacy RS, the RS for
demodulation of the sPDCCH and/or sPDSCH in an sTTI will be
referred to as an additional RS (A-RS) for simplicity of
description of the present invention.
[0186] The A-RS may be a UE-specific RS, and the UE may use only
the A-RS without the legacy CRS to demodulate the sPDCCH and/or
sPDSCH in an sTTI. Accordingly, UE-specific precoding may be
applied to the A-RS as in the case of the legacy DMRS so as to
transmit the A-RS. Such precoding may be identical to the precoding
applied to the sPDCCH and/or sPDSCH. Additionally, transmission of
the A-RS may also be UE-specific. The A-RS may be transmitted at
the subframe/PRB position which is UE-specifically configured or
defined in a standard document. Alternatively, the A-RS may be
transmitted only in the region of sTTI(s) and/or PRB(s) having the
sPDCCH and/or sPDSCH.
[0187] A UE using the A-RS is not allowed to use the legacy CRS and
the A-RS together to perform channel estimation for reception of
the sPDCCH and/or sPDSCH. If the A-RS is transmitted only in the
sTTI region in which the sPDCCH and/or sPDSCH is transmitted, the
UE is not allowed to use an A-RS transmitted in another sTTI for
channel estimation.
[0188] Specifically, the A-RS mentioned in this embodiment may
refer to the DMRS.
[0189] C. RS Usage 3: Legacy CRS+Additional RS
[0190] Using the legacy CRS alone may not provide sufficient
channel estimation performance due to shortage of the amount of RS
present in an sTTI. To address this issue, an additional RS (i.e.,
A-RS) may be used together with the legacy CRS to demodulate the
sPDCCH and/or sPDSCH in the sTTI.
[0191] Specifically, the A-RS mentioned in this disclosure may
refer to the DMRS.
[0192] --Cell-Specific A-RS
[0193] The A-RS used together with the legacy CRS to demodulate the
sPDCCH and/or sPDSCH may be a cell-specific RS. Specifically, such
A-RS may be transmitted at a subframe/PRB location which is
cell-specifically configured or defined in a standard document.
[0194] In this case, in order to perform demodulation of the
control/data channel transmitted in a specific sTTI, a CRS and A-RS
transmitted in another sTTI may be used (together with the CRS and
A-RS in the specific sTTI) for channel estimation. Accordingly,
channel estimation performance may be enhanced compared to the case
where only the CRS and A-RS transmitted in the sTTI are used to
perform channel estimation. In addition, since the legacy CRS is
also used for channel estimation, overhead of the additional RS may
be reduced.
[0195] In the legacy system, the UE is not notified of a precoding
matrix used for transmission of a PDSCH in transmission model 9
(hereinafter, TM9) or transmission of an EPDCCH, and thus the UE
receives the PDSCH/EPDCH without knowing the precoding matrix. In
order to use the CRC together with the A-RS for channel estimation,
the sPDCCH/sPDSCH may not be transmitted if the precoding matrix
used for transmission of the sPDCCH/sPDSCH is not announced to the
UE (or the UE does not recognize the precoding matrix), in contrast
with transmission of the legacy PDSCH in TM9 or transmission of the
EPDCCH. Accordingly, the UE needs to be aware of the precoding
matrix used for transmission of the sPDCCH/sPDSCH.
[0196] --UE-Specific A-RS
[0197] The A-RS used for demodulation of the sPDCCH and/or sPDSCH
along with the legacy CRS may be a UE-specific RS. Such A-RS may be
transmitted at a subframe/PRB location which is UE-specifically
configured or defined in a standard document. Alternatively, the
A-RS may be transmitted only in an sTTI and/or PRB region in which
the sPDCCH and/or sPDSCH is transmitted to the UE.
[0198] In this case, to demodulate a control/data channel
transmitted within a specific sTTI, a CRS transmitted within
another sTTI may be used (together with the CRS and A-RS in the
specific sTTI) for channel estimation. Accordingly, channel
estimation performance may be enhanced compared to the case where
only the CRS and A-RS transmitted in the specific sTTI are used to
perform channel estimation. In addition, since the legacy CRS is
also used for channel estimation, overhead of the additional RS may
be reduced.
[0199] However, in order to use the CRC along with the A-RS for
channel estimation, the sPDCCH/sPDSCH may not be transmitted if a
precoding matrix used for transmission of the sPDCCH/sPDSCH is not
announced to the UE (or the UE does not recognize the precoding
matrix), in contrast with transmission of the legacy PDSCH in TM9
or transmission of the EPDCCH. Accordingly, the UE needs to be
aware of the precoding matrix used for transmission of the
sPDCCH/sPDSCH.
[0200] --Indication of Precoding Matrix
[0201] When the legacy CRS and the A-RS are used together for
demodulation of the sPDCCH and/or sPDSCH, the precoding matrix
applied to the sPDSCH may be notified to the UE using the following
methods.
[0202] *Option 1. Fixed Precoding (SFBC)
[0203] The sPDSCH may be transmitted invariably using the transmit
diversity scheme (e.g., SFBC).
[0204] Option 2. Precoding Pattern (UE-Specific or
Cell-Specific)
[0205] The sPDSCH may be transmitted using a cell-specific
precoding pattern. Alternatively, if the precoding matrix is
determined by UE ID, the sPDSCH may be transmitted using a
UE-specific precoding pattern. In this case, the precoding matrix
used for transmission of the sPDSCH may be determined by the
entirety or a part of the following elements.
[0206] >PRB location of sPDSCH transmission,
[0207] >sTTI/subframe/SFN index of sPDSCH transmission,
[0208] >Cell ID or virtual cell ID configured by eNB, and
[0209] >UE ID.
[0210] *Option 3. Semi-Static Configuration by RRC
[0211] The precoding matrix used for sPDSCH may be semi-statically
configured for the UE through RRC.
[0212] *Option 4. Dynamic Configuration by Legacy PDCCH
[0213] The precoding matrix used for the sPDSCH may be dynamically
configured by the legacy PDCCH. In this case, a precoding matrix
configured on the legacy PDCCH may be applied only in a subframe in
which the sPDCCH is transmitted. Alternatively, the precoding
matrix may be persistently applied until the precoding matrix is
configured by a new legacy PDCCH next time.
[0214] *Option 5. Dynamic Configuration by sPDCCH
[0215] The precoding matrix applied to the sPDSCH may be
dynamically configured by DCI (carried by the PDCCH or sPDCCH) for
scheduling the sPDSCH.
[0216] When the legacy CRS and the A-RS are used together for
demodulation of the sPDCCH and/or sPDSCH, the precoding matrix
applied to the sPDSCH may be notified to the UE using the following
methods.
[0217] *Option 1. Fixed Precoding (SFBC)
[0218] The sPDSCH may be transmitted invariably using the transmit
diversity scheme (e.g., SFBC).
[0219] *Option 2. Precoding Pattern (UE-Specific or
Cell-Specific)
[0220] The sPDSCH may be transmitted using a cell-specific
precoding pattern. Alternatively, if the precoding matrix is
determined by UE ID, the sPDSCH may be transmitted using a
UE-specific precoding pattern. In this case, the precoding matrix
used for transmission of the sPDSCH may be determined by the
entirety or a part of the following elements.
[0221] >PRB location of sPDCCH transmission,
[0222] >sTTI/subframe/SFN index of sPDCCH transmission,
[0223] >Cell ID or virtual cell ID configured by eNB, and
[0224] >UE ID.
[0225] *Option 3. Semi-Static Configuration by RRC
[0226] The precoding matrix used for sPDSCH may be semi-statically
configured for the UE through RRC.
[0227] *Option 4. Dynamic configuration by legacy PDCCH
[0228] The precoding matrix used for the sPDSCH may be dynamically
configured by the legacy PDCCH. In this case, a precoding matrix
configured by the legacy PDCCH may be applied only in a subframe in
which the sPDCCH is transmitted. Alternatively, the precoding
matrix may be persistently applied until the precoding matrix is
configured by a new legacy PDCCH next time.
[0229] The A-RS may be additionally transmitted in an OFDM symbol,
in which the CRS is not transmitted, in the region of OFDM
symbol(s) in which the sPDCCH/sPDSCH is transmitted. Alternatively,
the A-RS may be transmitted if a CRS RE is not present in the
region of OFDM symbol(s) in which the sPDCCH/sPDSCH is
transmitted.
[0230] The legacy CRS is not transmitted in the MBSFN region of an
MBSFN subframe. Accordingly, the A-RS is not transmitted in a
subframe in which the CRS is transmitted. If sPDCCH/sPDSCH is
transmitted in a subframe (e.g., MBSFN subframe) in which the CRS
is not transmitted (in a region except the legacy control region),
the A-RS may be transmitted. In this case, the UE may assume that
the sTTI-based sPDCCH/sPDSCH is not transmitted in the MBSFN
subframe. Alternatively, the UE may assume that sTTI-based
transmission is supported in the MBSFN subframe, but only the A-RS
is transmitted without transmission of the legacy CRS in a region
(e.g., the MBSFN region of the MBSFN subframe) except the legacy
control region. The A-RS may be transmitted in 1) the entire region
of PRB(s), 2) a region of (fixed or higher-layer signaled) PRB(s)
in which the sTTI-based operation is performed, or 3) a region of
PRB(s) in which the sPDCCH and/or sPDSCH is transmitted. In this
case, an RS conforming to the legacy CRS sequence and RS RE pattern
and the A-RS may be transmitted together in the MBSFN subframe.
Herein, the RS conforming to the legacy CRS sequence and RS RE
pattern may be transmitted in 1) the entire region of PRB(s), 2) a
region of (fixed or higher-layer signaled) PRB(s) in which the
sTTI-based operation is performed, or 3) a region of PRB(s) in
which the sPDCCH and/or sPDSCH is transmitted. In addition, the
A-RS may be transmitted using 1) determined RE locations in the
entire region of OFDM symbol(s), 2) determined RE locations in a
region of OFDM symbol(s) in which the sPDCCH/sPDSCH is transmitted,
or 3) determined RE locations in an sTTI region in which the
sPDCCH/sPDSCH is transmitted, or 4) determined RE locations in a
first OFDM symbol region in which the sPDCCH/sPDSCH is
transmitted.
[0231] Specifically, the pattern of the A-RS may be defined in
units of an OFDM symbol within one PRB. FIG. 11 illustrates a
demodulation reference signal (DMRS) within one OFDM symbol. For
example, the A-RS may be transmitted/received within one PRB in a
pattern shown in FIG. 11. The A-RS pattern proposed in this
embodiment includes a form obtained through frequency-shift, namely
v-shift of the pattern of FIG. 11. The v-shift value of the A-RS
pattern may depend on the cell ID, UE ID, OFDM symbol index, sTTI
index, and/or subframe index. Alternatively, the pattern of the
A-RS may be identical to the CRS pattern transmitted on OFDM symbol
#0. The A-RS pattern may be used within PRB and OFDM symbol regions
in which the A-RS is transmitted.
[0232] Alternatively, the pattern of the A-RS may be defined within
one PRB in units of a subframe. For example, the locations of REs
occupied by the A-RS may have a pattern similar to that of the
legacy CRS, and the A-RS may use the legacy CRS pattern, but may be
transmitted only within a time/frequency region in which the A-RS
is actually transmitted. In this case, transmission of the A-RS may
be punctured in a time/frequency region in which the A-RS is not
transmitted. Additionally, the A-RS may have the legacy CRS
pattern, but may have another v-shift value. The V-shift value of
the A-RS pattern may depend on the cell ID, UE ID, OFDM symbol
index, sTTI index, and/or subframe index.
[0233] When the sPDCCH/sPDSCH transmitted based on the DMRS is
supported, additional transmission of the DMRS in a region of OFDM
symbol(s) used for CRS transmission or a region of subframe(s)
having the CRS may raise an issue in terms of overhead. However, if
the sPDCCH/sPDSCH is transmitted based only on the CRS, it may not
be properly transmitted in a region of OFDM symbol/subframe(s) in
which the CRS is not transmitted.
[0234] To address this issue, the present invention proposes that
the sPDCCH/sPDSCH be transmitted based on the CRS in the case where
the sPDCCH/sPDSCH is transmitted in OFDM symbol(s) with the CRS or
OFDM symbols including an OFDM symbol with the CRS and that the
sPDCCH/sPDSCH be transmitted based on the DMRS in the case where
the sPDCCH/sPDSCH is transmitted in the OFDM symbols in which the
CRS is not transmitted or transmitted using only the OFDM symbols
with no CRS. In other words, if the sPDCCH/sPDSCH is received in
OFDM symbol(s) having the CRS or in OFDM symbol(s) including the
OFDM symbols having the CRS, the sPDCCH/sPDSCH may be received,
demodulated or decoded (hereinafter, received/demodulated/decoded)
based on the CRS. If the sPDCCH/sPDSCH is received in OFDM
symbol(s) without the CRS or only in OFDM symbols without the CRS,
the sPDCCH/sPDSCH may be received/demodulated/decoded based on the
DMRS.
[0235] Alternatively, the sPDCCH/sPDSCH may be transmitted based on
the CRS if it is transmitted in a subframe in which the CRS is
transmitted, and may be transmitted based on the DMRS if it is
transmitted in a subframe (e.g., MBSFN subframe) in which the CRS
is not transmitted (in a region except the legacy control region).
In the case of the MBSFN subframe, since the CRS is transmitted in
the legacy control region (i.e., a non-MBSFN region), an sPDCCH
transmitted through the legacy control region may be transmitted
based on the CRS.
[0236] Herein, transmitting the sPDCCH/sPDSCH based on the CRS may
mean that a CRS-based transmission scheme (e.g., single port
transmission, SFBC (transmit diversity) transmission) is used to
transmit the sPDCCH/sPDSCH and that the UE uses the CRS to perform
sPDCCH/sPDSCH demodulation. Transmitting the sPDCCH/sPDSCH based on
the DMRS may mean that a DMRS-based transmission scheme (e.g.,
single port transmission (localized transmission of EPDCCH),
distributed transmission of the EPDCCH, or a transmission scheme
used in TM7/8/9/10) is used to transmit the sPDCCH/sPDSCH, and the
UE uses the DMRS to perform sPDCCH/sPDSCH demodulation.
[0237] In the case where a DMRS based transmission mode (e.g., TM7,
TM8, TM9 or TM10) is configured, transmitting the CRS and the DMRS
together may raise an issue of RS overhead. Accordingly, to prevent
the overhead issue caused by simultaneous transmission of the DMRS
and the CRS, the UE may operate in a CRS based TM (e.g., TM2) in a
non-MBSFN subframe even though a DMRS based TM is configured for
the UE. In this case, upon receiving the configuration of the DMRS
based TM, the UE may assume that the sPDSCH is transmitted in the
DMRS based TM in the MBSFN subframe and that the sPDSCH operates in
the CRS based TM in the non-MBSFN subframe. Similarly, for the
sPDCCH, if DMRS based sPDCCH transmission is configured, the sPDCCH
may be transmitted based on the DMRS in the MBSFN subframe, and
transmitted based on the CRS in the non-MBSFN subframe.
Alternatively, only a CRS based TM may be configured/used in the
non-MBSFN subframe, and only a DMRS based TM may be configured/used
in the MBSFN subframe.
[0238] Specifically, operation may be performed in the DMRS based
TM in the MBSFN subframe, and whether to operate in the CRS based
TM or DMR based TM in the non-MBSFN subframe may be determined
according to the number of antenna ports (or the number of data
transmission layers) used for transmission in an sTTI or subframe.
For example, the DMRS based TM may be applied if P or fewer antenna
ports are used to transmit data, and the CRS based TM may be
applied if more than P antenna ports are used to transmit data. In
contrast, the CRS based TM may be applied if P or fewer antenna
ports are used to transmit data, and the DMRS based TM may be
applied if more than P antenna ports are used to transmit data.
[0239] FIG. 12 illustrates examples of configuration of sTTI(s) in
consideration of a legacy PDCCH region and CRS.
[0240] Some of the OFDM symbol(s) constituting an sTTI may be
included in the legacy control region (i.e., the region of OFDM
symbol(s) in which the legacy PDCCH is transmitted). Alternatively,
due to the legacy control region or for other reasons, the region
of available OFDM symbol(s) in an sTTI may be smaller than that in
the typical sTTI as in the case of an sTTI with one OFDM symbol.
For example, the number of available OFDM symbols is as small as 1
in TTI0 of the TTI(s) illustrated in FIG. 12(a), TTI1 of the TTI(s)
illustrated in FIG. 12(d), or TTI1 of the TTI(s) illustrated in
FIG. 12(e). Transmitting all DMRSs for the sPDSCH in an sTTI region
having a small number of available OFDM symbols may result in
significant overhead. Accordingly, the present invention proposes
that the UE receiving configuration of a DMRS based TM for
transmission of the sPDSCH assume that the sPDSCH is transmitted in
the CRS based TM in an sTTI consisting of a small number of OFDM
symbols. That is, if a DMRS based TM is configured to be used for
transmission of the sPDSCH, fallback to a CRS based TM may be
implemented in an sTTI having a small number (e.g., 1) of available
OFDM symbols.
[0241] D. Detailed RS Patterns
[0242] In this section, specific RS pattern(s) for applying the
aforementioned "RS usages" are discussed.
[0243] --RS Pattern for `RS Usage 2: Additional RS Only`
[0244] When an RS for demodulation of the sPDCCH and/or sPDSCH in
an sTTI is not the legacy CRS but a UE-specific A-RS, RS pattern(s)
depending on the TTI length may be used.
[0245] # Case 1: The TTI Length Equals One OFDM Symbol
[0246] When the TTI length equals one OFDM symbol, the A-RS may be
present in every sTTI because the UE needs to perform demodulation
of the sPDCCH/sPDSCH using only the A-RS present in the sTTI region
in which the sPDCCH/sPDSCH is transmitted.
[0247] *Option 1. When Two APs are Supported and the RS RE Location
Differs Between the APs
[0248] When it is assumed that two antenna ports (antenna ports
(APs) 7 and 8) are used for transmission of the A-RS, and A-RSs to
be transmitted through AP 7 and AP 8 are transmitted through
different REs, the RE location(s) of the A-RSs may be given as
shown in FIG. 13. In FIG. 13, A-RS 7 denotes the A-RS transmitted
through AP 7, and A-RS 8 denotes the A-RS transmitted through AP 8.
The A-RS may be present at the same RE location in every sTTI, and
may be positioned at a location different from the RE location of
transmission of the legacy CRS. When the RE location of the CRS
changes, the RE locations of the A-RSs also change. FIGS. 13(a),
13(b) and 13(c) illustrate examples of an RS pattern in which the
A-RS is present at 2 REs for each AP within one PRB in every sTTI.
FIGS. 13(a), 13(b) and 13(c) show RE locations of the A-RS when the
value of v-shift, which determines the RE location of the legacy
CRS, is 0, 1 and 2, respectively. FIGS. 13(d), 13(e) and 13(f)
illustrate examples of an RS pattern in which the A-RS is present
at one RE for each AP within one PRB in every sTTI. FIGS. 13(d),
13(e) and 13(f) show A-RS locations when the value of v-shift,
which determines the RE location of the legacy CRS, is 0, 1 and 2,
respectively.
[0249] The RS pattern(s) according to the present invention include
an RS pattern with the RE locations of A-RS 7 and A-RS 8 switched
for the A-RS pattern proposed above. In addition, the RS pattern(s)
according to the present invention may be applied even when an AP
different from AP 7 and AP 8 is used for transmission of the
A-RS.
[0250] *Option 2. When Two APs are Supported and the Same RS RE
Location is Given for the APs
[0251] Two antenna ports (AP 7 and AP 8) may be used to transmit
A-RSs, and the A-RSs to be transmitted through AP 7 and AP 8 may be
transmitted through the same RE location. In this case, similar to
the case where the DMRS for AP 7 and the DMRS for AP 8 are
transmitted in the CDM manner through the same RE location using
orthogonal codes, the A-RS for AP 7 and the A-RS for AP 8 may be
transmitted in the CDM manner through the same RE location using
orthogonal codes.
[0252] In this case, the RE location(s) of the A-RSs may be given
as shown in FIG. 14. In FIG. 14, A-RS 7 denotes the A-RS
transmitted through AP 7, and A-RS 8 denotes the A-RS transmitted
through AP 8. The A-RS may be present at the same RE location in
every sTTI, and be positioned at an RE location different from the
RE location of transmission of the legacy CRS. When the RE location
of the CRS changes, the RE location of the A-RS also changes. FIGS.
14(a), 14(b) and 14(c) illustrate examples of an RS pattern in
which the A-RS is present at 4 REs for each AP within one PRB in
every sTTI. FIGS. 14(a), 14(b) and 14(c) show RE locations of the
A-RS when the value of v-shift, which determines the RE location of
the legacy CRS, is 0, 1 and 2, respectively. FIGS. 14(d), 14(e) and
14(f) illustrate examples of an RS pattern in which the A-RS is
present at 2 REs for each AP within one PRB in every sTTI. FIGS.
14(d), 14(e) and 14(f) show RE locations of the A-RS when the value
of v-shift, which determines the RE location of the legacy CRS, is
0, 1 and 2, respectively. In this case, the A-RSs may be
transmitted at two A-RS REs which are present at neighboring RE
locations in the same sTTI, by applying orthogonal codes to A-RS AP
7 and A-RS AP 8. For example, A-RS 7 may be transmitted by
multiplying an RS RE on subcarrier i and an RS RE on subcarrier i+1
by w0 and w1, respectively. Herein, [w0, w1]=[1, 1]. In addition,
A-RS 8 may be transmitted by multiplying an RS RE on subcarrier i
and an RS RE on subcarrier i+1 by w0 and w1, respectively. In this
case, [w0, w1]=[1, -1].
[0253] The same principle is applicable even when an AP different
from AP 7 and AP 8 is used to transmit the A-RSs.
[0254] # Case 2: The TTI Length Equals 2 OFDM Symbols
[0255] When the TTI length equals 2 OFDM symbols, an A-RS may be
present in every sTTI because the UE needs to perform demodulation
of the sPDCCH/sPDSCH using only A-RSs present in the sTTI region in
which the sPDCCH/sPDSCH is transmitted.
[0256] *Option 1. When Two APs are Supported and the RS RE Location
Differs Between the APs
[0257] When it is assumed that two antenna ports (AP 7 and AP 8)
are used for transmission of A-RSs, and A-RSs to be transmitted
through AP 7 and AP 8 are transmitted through different REs, the RE
location(s) of the A-RSs may be given as shown in FIGS. 15 to 17.
In FIGS. 15 to 17, A-RS 7 denotes the A-RS transmitted through AP
7, and A-RS 8 denotes the A-RS transmitted through AP 8. The A-RSs
may be present at the same RE location in every sTTI, but may not
be positioned at the RE location of transmission of the legacy CRS.
If the RE location of the A-RS is within an OFDM symbol on which
the legacy CRS is transmitted, the RE location of the A-RS may be
v-shifted or changed according to the RE location of the CRS
(according to the value of v-shift). If the RE location of the
A-RSs is only within an OFDM symbol in which the legacy CRS is not
transmitted, the A-RS may be positioned at the same RE location
irrespective of the RE location (the v-shift value) of the CRS.
[0258] FIG. 15 illustrates examples of an RS pattern in which the
A-RS is present at 4 REs for each AP within one PRB in every sTTI.
FIG. 16 illustrates examples of an RS pattern in which the A-RS is
present at 3 REs for each AP within one PRB in every sTTI. FIG. 17
illustrates examples of an RS pattern in which the A-RS is present
at 2 REs for each AP within one PRB in every sTTI.
[0259] The A-RS pattern(s) according to the present invention
include an RS pattern with the RE locations of A-RS 7 and A-RS 8
switched for the A-RS pattern proposed above. In addition, the RS
pattern(s) according to the present invention may be applied even
when an AP different from AP 7 and AP 8 is used for transmission of
an A-RS. Further, the A-RS pattern(s) according to the present
invention includes an RE pattern obtained by v-shifting the A-RS
pattern proposed above.
[0260] *Option 2. When Two APs are Supported and the Same RS RE
Location is Given for the APs
[0261] In consideration of the case where two antenna ports (AP 7
and AP 8) are used for transmission of A-RSs, the A-RSs to be
transmitted through AP 7 and AP 8 may be transmitted at the same RE
location. In this case, similar to the case where the DMRS for AP 7
and the DMRS for AP 8 are transmitted in the CDM manner through the
same RE location using orthogonal codes, the A-RS for AP 7 and the
A-RS for AP 8 may be transmitted in the CDM manner through the same
RE location using orthogonal codes.
[0262] In this case, the RE location(s) of the A-RSs may be given
as shown in FIGS. 18 to 21. In FIGS. 18 to 21, A-RS 7 denotes an
A-RS transmitted through AP 7, and A-RS 8 denotes an A-RS
transmitted through AP 8. The A-RS may be present at the same RE
location in every sTTI, but may not be positioned at the RE
location of transmission of the legacy CRS. If the RE location of
the A-RS is within an OFDM symbol in which the legacy CRS is
transmitted, the RE location of the A-RS may be v-shifted or
changed according to the RE location of the CRS, namely, the value
of v-shift. If the RE location of the A-RS is only within an OFDM
symbol in which the legacy CRS is not transmitted, the A-RS may be
positioned at the same RE location irrespective of the RE location
of the CRS or the v-shift value.
[0263] FIG. 18 illustrates examples of an RS pattern in which the
A-RS is present at 8 REs for each AP within one PRB in every sTTI.
FIG. 19 illustrates examples of an RS pattern in which the A-RS is
present at 6 REs for each AP within one PRB in every sTTI. FIG. 20
illustrates examples of an RS pattern in which the A-RS is present
at 4 REs for each AP within one PRB in every sTTI. FIG. 21
illustrates examples of an RS pattern in which the A-RS is present
at 2 REs for each AP within one PRB in every sTTI. In the same
sTTI, the A-RS may be transmitted at two A-RS REs present at
neighboring RE locations (e.g., "the same subcarrier and
neighboring OFDM symbols" or "neighboring subcarriers and the same
OFDM symbol") by applying orthogonal codes to A-RS AP 7 and A-RS AP
8. For example, when the RS is positioned at two neighboring REs,
namely, RE i and RE i+1, A-RS 7 may be transmitted by multiplying
the RS transmitted at RE i and RE i+1 by w0 and w1. In this case,
[w0, w1]=[1, 1]. A-RS 8 may be transmitted by multiplying the RS
transmitted at RE i and RE i+1 by w0 and w1, respectively. In this
case, [w0, w1]=[1, -1].
[0264] The A-RS pattern(s) according to the present invention are
applicable even when an AP different from AP 7 and AP 8 is used to
transmit an A-RS.
[0265] *Option 3. When 4 APs are Supported
[0266] 4 antenna ports (AP 7, AP 8, AP 9, and AP 10) may be used to
transmit the A-RS. As in the case of the legacy DMRS, the A-RS for
AP 7 and the A-RS for AP 8 may be transmitted at the same RE
location, and the A-RS for AP 9 and the A-RS for AP 10 may be
transmitted at the same RE location. In this case, similar to the
conventional case where the DMRS for AP 7 and the DMRS for AP 8 are
transmitted in the CDM manner through the same RE location using
orthogonal codes, and the DMRS for AP 9 and the DMRS for AP 10 are
transmitted in the CDM manner through the same RE location using
orthogonal codes, the A-RS for AP 7 and the A-RS for AP 8 may be
transmitted in the CDM manner through the same RE location using
orthogonal codes, and the A-RS for AP 9 and the A-RS for AP 10 may
be transmitted in the CDM manner through the same RE location using
orthogonal codes.
[0267] In this case, the RE location(s) of the A-RSs may be given
as shown in FIG. 22. In FIG. 22, A-RS 7, A-RS 8, A-RS 9, and A-RS
10 denote the A-RSs transmitted through AP 7, AP 8, AP 9, and AP
10, respectively. The A-RSs may be present at the same RE location
in every sTTI, but may not be positioned at the RE location of
transmission of the legacy CRS. The RE location of the A-RSs may be
v-shifted or changed according to the RE location of the CRS (or
according to the value of v-shift).
[0268] FIGS. 22(a), 22(b) and 22(c) illustrate examples of an RS
pattern in which the A-RS is present at 4 REs for each AP within
one PRB in every sTTI. FIGS. 22(d), 22(e) and 22(f) illustrate
examples of an RS pattern in which the A-RS is present at 2 REs for
each AP within one PRB in every sTTI. FIGS. 22(a), 22(b) and 22(c)
show A-RS locations when the value of v-shift, which determines the
RE location of the legacy CRS, is 0, 1 and 2, respectively. FIG.
22(d), FIG. 22(e) and FIG. 22(f) show A-RS locations when the value
of v-shift, which determines the RE location of the legacy CRS, is
0, 1 and 2, respectively. The A-RS pattern(s) according to the
present invention may be applied even when an AP different from AP
7, AP 8, AP 9 and AP 10 is used for transmission of the A-RSs.
Further, the A-RS pattern(s) according to the present invention
includes RE pattern(s) obtained by v-shifting the A-RS pattern
proposed above.
[0269] # Case 3: The TTI Length Equals 3 OFDM Symbols
[0270] When the TTI length equals 3 OFDM symbols, the A-RS may be
present in every sTTI because the UE needs to perform demodulation
of the sPDCCH/sPDSCH using only A-RSs present in the sTTI region in
which the sPDCCH/sPDSCH is transmitted.
[0271] When the TTI length equals 3 OFDM symbols, the RS pattern
proposed for the case where the TTI length equals 2 OFDM symbols
may be employed. In this case, the RS, which is configured to be
transmitted through 2 OFDM symbols in a two-OFDM symbol sTTI in the
previous case, may be transmitted through 2 OFDM symbols in a
three-OFDM symbol sTTI. For example, the OFDM symbols having the
A-RS may be the first and second OFDM symbols in the sTTI.
Similarly, the RS, which is configured to be transmitted through
one OFDM symbol in a two-OFDM symbol sTTI, may be transmitted
through one OFDM symbol in a three-OFDM symbol sTTI. For example,
an OFDM symbol having the A-RS may be the first OFDM symbol in the
sTTI.
[0272] 4 antenna ports (AP 7, AP 8, AP 9, and AP 10) may be used to
transmit the A-RS. As in the case of the legacy DMRS, the A-RS for
AP 7 and the A-RS for AP 8 may be transmitted at the same RE
location, and the A-RS for AP 9 and the A-RS for AP 10 may be
transmitted at the same RE location. In this case, similar to the
conventional case where the DMRS for AP 7 and the DMRS for AP 8 are
transmitted in the CDM manner through the same RE location using
orthogonal codes, and the DMRS for AP 9 and the DMRS for AP 10 are
transmitted in the CDM manner through the same RE location using
orthogonal codes, the A-RS for AP 7 and the A-RS for AP 8 may be
transmitted in the CDM manner through the same RE location using
orthogonal codes, and the A-RS for AP 9 and the A-RS for AP 10 may
be transmitted in the CDM manner through the same RE location using
orthogonal codes.
[0273] In this case, the RE location(s) of the A-RSs may be given
as shown in FIGS. 23, 24 and 25. In FIGS. 23, 24 and 25, A-RS 7,
A-RS 8, A-RS 9, and A-RS 10 denote the A-RSs transmitted through AP
7, AP 8, AP 9, and AP 10, respectively. The A-RSs may be present at
the same RE location in every sTTI, but may not be positioned at
the RE location of transmission of the legacy CRS. The RE location
of the A-RSs may be v-shifted or changed according to the RE
location of the CRS (or according to the value of v-shift).
Specifically, in order to position the A-RS on an OFDM symbol in
which the legacy CRS is not transmitted, the A-RS may be
transmitted through the first and second OFDM symbols in each of
the first sTTI (OFDM symbols #2-#4) and the second sTTI (OFDM
symbols #5-#7) within a subframe, and be transmitted through the
second and third OFDM symbols in each of the third sTTI (OFDM
symbols #8-#10) and fourth sTTI (OFDM symbols #11-#13) within the
same subframe.
[0274] FIG. 23 illustrates examples of an RS pattern in which the
A-RS is present at 6 REs for each AP within one PRB in every sTTI.
FIG. 24 illustrates examples of an RS pattern in which the A-RS is
present at 4 REs for each AP within one PRB in every sTTI. FIG. 25
illustrates examples of an RS pattern in which the A-RS is present
at 2 REs for each AP within one PRB in every sTTI. The A-RS
pattern(s) according to the present invention may be applied even
when an AP different from AP 7, AP 8, AP 9 and AP 10 is used for
transmission of the A-RSs. Further, the A-RS pattern(s) according
to the present invention include RE pattern(s) obtained by
v-shifting the A-RS pattern proposed above.
[0275] # Case 4: The TTI Length Equals 4 OFDM Symbols
[0276] When the TTI length equals 4 OFDM symbols, an A-RS may be
present in every sTTI because the UE needs to perform demodulation
of the sPDCCH/sPDSCH using only A-RSs present in the sTTI region in
which the sPDCCH/sPDSCH is transmitted.
[0277] When the TTI length equals 4 OFDM symbols, the RS pattern
proposed for the case where the TTI length equals 2 OFDM symbols
may be employed. In this case, the RS, which is configured to be
transmitted through 2 OFDM symbols in a two-OFDM symbol sTTI in the
previous case, may be transmitted through 2 OFDM symbols in a
four-OFDM symbol sTTI. For example, the OFDM symbols having the
A-RS may be the first and second OFDM symbols in the sTTI.
Similarly, the RS, which is configured to be transmitted through
one OFDM symbol in a two-OFDM symbol sTTI, may be transmitted
through one OFDM symbol in a four-OFDM symbol sTTI. For example, an
OFDM symbol having the A-RS may be the first OFDM symbol in the
sTTI.
[0278] For example, when the RS pattern proposed for the case where
the TTI length equals 2 OFDM symbols as shown in FIGS. 15(d), 15(e)
and 15(f) is applied to the first and second OFDM symbols in the
four-OFDM symbol sTTI, an RS pattern shown in FIG. 26 may be
applied.
[0279] RS Pattern for `RS Usage 3: Legacy CRS+Additional RS`
[0280] When a cell-specific or UE-specific A-RS and the legacy CRS
are used together as RSs for demodulation of the sPDCCH and/or
sPDSCH in an sTTI, RS pattern(s) depending on the TTI length may be
used.
[0281] When a cell-specific or UE-specific A-RS and the legacy CRS
are used together as RSs for demodulation of the sPDCCH and/or
sPDSCH in an sTTI, the RS pattern(s) proposed in the subsection "RS
pattern for `RS usage 3: Legacy CRS+additional RS" may be used as
RS pattern(s) of the A-RS.
[0282] Additionally, the following RS pattern may be used for
transmission of the A-RS. In this embodiment, to reduce the RS
overhead and/or to make sTTIs have similar RS overhead (considering
the legacy CRS and A-RS), presence/absence of the A-RS and/or the
number of REs may be configured differently for each sTTI. If the
legacy CRS and the A-RS are used together for channel estimation,
the UE may perform channel estimation using the legacy CRS or A-RS
transmitted in a neighboring sTTI, even if the number of the A-RSs
transmitted is small or no A-RS is transmitted in one sTTI.
[0283] If two antenna ports are used for transmission of the A-RSs,
AP 0 and AP 1 through which the A-RSs are transmitted may be
identical to AP 7 and AP 8. Alternatively, AP x and AP y through
which the A-RSs are transmitted may have a quasi co-located (QCL)
relationship with AP 0 and AP 1.
[0284] # Case 1: The TTI Length Equals One OFDM Symbol
[0285] When the TTI length equals one OFDM symbol, the following RS
pattern(s) may be used to transmit A-RSs.
[0286] In FIGS. 27, 28 and 29, A-RS 0 denotes the A-RS transmitted
through AP 0, and A-RS 1 denotes the A-RS transmitted through AP
1.
[0287] As shown in FIG. 27, at least 2 RS REs per antenna port may
be present in each sTTI, including the A-RS and the legacy CRS. In
this case, the A-RS may not be transmitted on OFDM symbols #0, #1,
#4, #7, #8 and #11 since the legacy CRS is transmitted at 2 REs per
OFDM symbol for each antenna port. On OFDM symbol #8 (and/or OFDM
symbol #1), however, the legacy CRS for AP 2 and the legacy CRS for
AP 3 are transmitted, and thus A-RSs using AP 0 and AP 1 are not
transmitted.
[0288] *Option 1. To allow 2 RS REs to be used per antenna port in
each sTTI, RE locations where the legacy CRS is not transmitted may
be used to transmit each of the A-RSs for AP 0 and AP 1 at 2
REs.
[0289] *Option 2. To maintain the same RS overhead in each sTTI,
the A-RS may not be transmitted on corresponding OFDM symbols.
[0290] Additionally, if the number of antenna ports through which
the CRS is transmitted is 2, the RE location for the legacy CRS is
used to transmit each of the A-RSs for AP 0 and AP 1 at 2 REs on
OFDM symbol #8 (and/or OFDM symbol #1). If the number of antenna
ports through which the CRS is transmitted is 4, the A-RS may not
be transmitted on OFDM symbol #8 (and/or OFDM symbol #1).
[0291] At least one RS RE per antenna port may be present in each
sTTI, including the A-RS and the legacy CRS. For example, the A-RS
patterns of FIG. 28 may be used. In this case, the A-RS may not be
transmitted on OFDM symbols #0, #1, #4, #7, #8 and #11 since the
legacy CRS is transmitted at 2 REs per OFDM symbol for each antenna
port. On OFDM symbol #8 (and/or OFDM symbol #1), however, the
legacy CRS for AP 2 and the legacy CRS for AP 3 are transmitted,
and thus none of the A-RSs using AP 0 and AP 1 are transmitted. On
such OFDM symbol, the following A-RS may be transmitted.
[0292] *Option 1. To allow one RS RE to be transmitted per antenna
port in each sTTI, RE locations where the legacy CRS is not
transmitted may be used to transmit each of the A-RSs for AP 0 and
AP 1 corresponding to one RE.
[0293] *Option 2. To maintain as equal RS overhead as possible in
each sTTI, the A-RS may not be transmitted on corresponding OFDM
symbols.
[0294] Additionally, if the number of antenna ports through which
the CRS is transmitted is 2, the RE location for transmission of
the legacy CRS is used to transmit each of the A-RSs for AP 0 and
AP 1 at 2 REs on OFDM symbol #8 (and/or OFDM symbol #1). If the
number of antenna ports through which the CRS is transmitted is 4,
the A-RS may not be transmitted on OFDM symbol #8 (and/or OFDM
symbol #1).
[0295] At least 2 RS REs per antenna port may be present in
neighboring sTTIs, including the A-RS and the legacy CRS. For
example, the RS pattern of FIG. 29 may be used. The A-RSs may be
positioned, such that two or more RS REs are not transmitted per AP
in one sTTI, while at least 2 RS REs are present per antenna port
in two neighboring sTTI.
[0296] The A-RS pattern(s) according to the present invention
include an RS pattern with the RE locations of A-RS 0 and A-RS 1
switched for the A-RS pattern proposed above. In addition, the A-RS
pattern(s) according to the present invention may be applied even
when an AP different from AP 0 and AP 1 is used for transmission of
the A-RSs.
[0297] # Case 2: The TTI Length Equals 2 OFDM Symbols
[0298] When the TTI length equals 2 OFDM symbols, the following RS
pattern(s) may be used to transmit A-RSs.
[0299] In FIG. 30, A-RS 0 denotes the A-RS transmitted through AP
0, and A-RS 1 denotes the A-RS transmitted through AP 1. FIGS.
30(a), 30(b) and 30(c) show RE locations of the A-RS when the value
of v-shift, which determines the RE location of the legacy CRS, is
0, 1 and 2, respectively. FIGS. 30(d), 30(d) and 30(e) show RE
locations of the A-RS when the value of v-shift, which determines
the RE location of the legacy CRS, is 0, 1 and 2, respectively.
[0300] At least 4 RS REs per antenna port may be present in each
sTTI, including the A-RS and the legacy CRS. For example, the RS
pattern(s) of FIGS. 30(a), 30(b) and 30(c) may be used. In this
case, the A-RS may be transmitted at two REs per antenna port in
the second, third, fourth and fifth sTTIs in the region of sTTIs
except the two OFDM symbols forming the legacy PDCCH region because
the legacy CRS is transmitted on 4 REs per sTTI. In the fourth
sTTI, only the legacy CRSs for AP 2 and AP 3 are transmitted, and
thus the A-RS may be transmitted in the sTTI having only CRSs for
some of the 4 APs in the following manner.
[0301] *Option 1. To allow 4 RS REs to be used per antenna port in
each sTTI, RE locations where the legacy CRS is not transmitted may
be used to transmit each of the A-RSs for AP 0 and AP 1 at 4
REs.
[0302] *Option 2. To maintain the same RS overhead in each sTTI, an
A-RS may be transmitted at 2 REs per AP in the corresponding
sTTI.
[0303] Additionally, if the number of antenna ports through which
the CRS is transmitted is 2, each of the A-RSs for AP 0 and AP 1
may also be transmitted on 4 REs in the fourth sTTI region. If the
number of antenna ports through which the CRS is transmitted is 4,
an A-RS may be transmitted at 2 REs per AP.
[0304] At least 2 RS REs per antenna port may be present in each
sTTI, including the A-RS and the legacy CRS. For example, the RS
pattern(s) of FIGS. 30(d), 30(e) and 30(f) may be used. In this
case, the A-RS may not be transmitted in the second, third, fourth
and fifth sTTIs in the region of sTTIs except the two OFDM symbols
over which the legacy PDCCH region spans because the legacy CRS is
transmitted at 2 REs per sTTI in the second, third, fourth and
fifth sTTIs. In the fourth sTTI region, only the legacy CRSs for AP
2 and AP 3 are transmitted, and thus the A-RS may be transmitted in
the sTTI having only CRSs for some of the APs in the following
manner.
[0305] *Option 1. To allow 2 RS REs to be used per antenna port in
each sTTI, RE locations where the legacy CRS is not transmitted may
be used to transmit each of the A-RSs for AP 0 and AP 1 at 2
REs.
[0306] *Option 2. To maintain the same RS overhead in each sTTI, an
A-RS may not be transmitted in a corresponding sTTI.
[0307] Additionally, if the number of antenna ports through which
the CRS is transmitted is 2, each of the A-RSs for AP 0 and AP 1
may also be transmitted at 2 REs in the fourth sTTI region. If the
number of antenna ports through which the CRS is transmitted is 4,
the A-RS may not be transmitted in a corresponding sTTI.
[0308] The A-RS pattern(s) according to the present invention
include an RS pattern with the RE locations of A-RS 0 and A-RS 1
switched for the A-RS pattern proposed above. In addition, the A-RS
pattern(s) according to the present invention may be applied even
when an AP different from AP 0 and AP 1 is used for transmission of
the A-RSs.
[0309] # Case 3: The TTI Length Equals 3 OFDM Symbols
[0310] When the TTI length equals 3 OFDM symbols, the following RS
pattern(s) may be used to transmit A-RSs.
[0311] FIGS. 31(a), 31(b) and 31(c) show RE locations of the A-RS
when the value of v-shift, which determines the RE location of the
legacy CRS, is 0, 1 and 2, respectively. In FIG. 31, A-RS 0 denotes
the A-RS transmitted through AP 0, and A-RS 1 denotes the A-RS
transmitted through AP 1.
[0312] At least 4 RS REs per antenna port may be present in each
sTTI, including the A-RS and the legacy CRS. For example, the RS
pattern(s) of FIG. 31 may be used. Since the legacy CRS is
transmitted at 4 REs per sTTI, the A-RS may be transmitted at 2 REs
per antenna port in each sTTI. In the third TTI region, however,
only the legacy CRSs for AP 2 and AP 3 are transmitted, and thus
the A-RSs may be transmitted in the following manner.
[0313] *Option 1. To allow 4 RS REs to be used per antenna port in
each sTTI, RE locations where the legacy CRS is not transmitted may
be used to transmit each of the A-RSs for AP 0 and AP 1 at 4
REs.
[0314] *Option 2. To maintain the same RS overhead in each sTTI, an
A-RS may be transmitted at 2 REs per AP in a corresponding
sTTI.
[0315] Additionally, if the number of antenna ports through which
the CRS is transmitted is 2, each of the A-RSs for AP 0 and AP 1
may also be transmitted at 4 REs in the third sTTI region. If the
number of antenna ports through which the CRS is transmitted is 4,
an A-RS may be transmitted at 2 REs per AP.
[0316] The A-RS pattern(s) according to the present invention
include an RS pattern with the RE locations of A-RS 0 and A-RS 1
switched for the A-RS pattern proposed above. In addition, the A-RS
pattern(s) according to the present invention may be applied even
when an AP different from AP 0 and AP 1 is used for transmission of
the A-RSs.
[0317] # Case 4: The TTI Length Equals 4 OFDM Symbols
[0318] When the TTI length equals 4 OFDM symbols, the following RS
pattern(s) may be used to transmit A-RSs.
[0319] FIGS. 32(a), 32(b) and 32(c) show RE locations of the A-RS
when the value of v-shift, which determines the RE location of the
legacy CRS, is 0, 1 and 2, respectively. In FIG. 32, A-RS 0 denotes
the A-RS transmitted through AP 0, and A-RS 1 denotes the A-RS
transmitted through AP 1.
[0320] At least 4 RS REs per antenna port may be present in each
sTTI, including the A-RS and the legacy CRS. For example, the RS
pattern(s) of FIG. 32 may be used. The A-RS may be transmitted at 2
REs per antenna port in the first and third sTTI regions since the
legacy CRSs for AP 0 and AP 1 are transmitted at 4 REs per AP. In
the second sTTI region, however, the legacy CRSs for AP 0, AP 1, AP
2 and AP 3 are transmitted on 2 REs per AP, and thus the A-RSs may
be transmitted in the following manner.
[0321] *Option 1. To allow 4 RS REs to be used per antenna port in
each sTTI, RE locations where the legacy CRS is not transmitted may
be used to transmit each of the A-RSs for AP 0 and AP 1 at 2
REs.
[0322] *Option 2. To maintain the same RS overhead in each sTTI,
the A-RS may not be transmitted in a corresponding sTTI.
[0323] Additionally, if the number of antenna ports through which
the CRS is transmitted is 2, each of the A-RSs for AP 0 and AP 1
may also be transmitted at 2 REs in the second sTTI region. If the
number of antenna ports through which the CRS is transmitted is 4,
the A-RS may not be transmitted in the corresponding sTTI.
[0324] The A-RS pattern(s) according to the present invention
include an RS pattern with the RE locations of A-RS 0 and A-RS 1
switched for the A-RS pattern proposed above. In addition, the A-RS
pattern(s) according to the present invention may be applied even
when an AP different from AP 0 and AP 1 is used for transmission of
the A-RSs.
[0325] The A-RS pattern(s) described above may be used only on the
second OFDM symbol or the last the OFDM symbol in each sTTI. In
other words, only RS RE location(s) present on the second or last
OFDM symbol in each sTTI may be valid among the RS RE locations of
the A-RS pattern(s). For example, in the case of sTTIs each
consisting of 2 symbols, the a-RS may be present only within the
second OFDM symbol in each sTTI, and the A-RS pattern within the
second OFDM symbol may be identical to the positions of the RS RE
location (S) present on the second OFDM symbol in each sTTI among
the RS RE location(s) according to one of the A-RS patterns is
described above. For example, the A-RS patterns of FIGS. 22(a),
22(b) and 22(c) may be applied such that the A-RS is present only
on the second OFDM symbol in each sTTI as illustrated in FIGS.
33(a), 33(b) and 33(c).
[0326] The present invention is also applicable in cases where a
subframe has different sTTI configurations, for example, in the
case where 14 OFDM symbols are divided into a 3-OFDM symbol sTTI, a
2-OFDM symbol sTTI, a 2-OFDM symbol sTTI, a 3-OFDM symbol sTTI, a
2-OFDM symbol sTTI, and a 2-OFDM symbol sTTI, or in the case where
14 OFDM symbols are divided into a 3-OFDM symbol sTTI, a 2-OFDM
symbol sTTI, a 2-OFDM symbol sTTI, a 2-OFDM symbol sTTI, a 2-OFDM
symbol sTTI, and a 3-OFDM symbol sTTI.
[0327] E. A-RS Transmission within a Bundled PRBs
[0328] In order to reduce RS overhead according to transmission in
an sTTI, the A-RS of the present invention may be present only on
some PRBs. Specifically, the A-RS may be transmitted on one or Q
(Q<P) PRB(s) per P PRBs in an sTTI. For example, referring to
FIG. 34, the A-RS may be transmitted through one PRB per 4 PRBs in
an sTTI. Herein, the value of P and/or the value of Q may be fixed
or defined in a standard document, and be signaled by the eNB
through SIB or RRC.
[0329] In this case, the a-RS pattern in the region of PRB(s) in
which the a-RS is transmitted may be one of the RS patterns
described above.
[0330] F. sPDCCH DMRS
[0331] The DMRS for the sPDCCH (hereinafter, sPDCCH DMRS) may be
positioned within an OFDM symbol on which the sPDCCH is
transmitted. If the location of the OFDM symbol on which the sPDCCH
is transmitted is the first OFDM symbol in each sTTI, the sPDCCH
DMRS may be transmitted as shown in FIG. 35(a), 35(b) or 35(c), for
example. As shown in FIG. 35(a), 35(b) or 35(c), the sPDCCH DMRS
may be transmitted within one OFDM symbol on which the sPDCCH is
transmitted. In addition, the DMRSs for different antenna ports may
be transmitted at 2 REs contiguous in the frequency domain in a CDM
manner.
[0332] If the locations of the OFDM symbols on which the sPDCCH is
transmitted is the first two OFDM symbols in each sTTI, the sPDCCH
DMRS may be transmitted as shown in FIG. 35(a), 35(b), 35(c),
35(d), 35(e), 35(f) or 35(g), for example. As shown in FIG. 35(a),
35(b) or 35(c), the sPDCCH DMRS may be transmitted only within the
first OFDM symbol on which the sPDCCH is transmitted. In addition,
the DMRSs for different antenna ports may be transmitted at 2
contiguous REs in a CDM manner. Alternatively, as shown in FIG.
35(d), 35(e), 35(f) or 35(g), the DMRS may be transmitted through
two OFDM symbols on which the sPDCCH is transmitted. In addition,
the DMRSs for different antenna ports may be transmitted at 2 REs
contiguous in the time domain in a CDM manner.
[0333] FIG. 35 illustrates an sPDCCH DMRS in an sTTI whose length
equals 3 OFDM symbols. The present invention is also applicable to
an sTTI consisting of a different number of OFDM symbols and/or an
sTTI at another location.
[0334] The DMRS patterns according to an embodiment of the present
invention include DMRS pattern(s) obtained by v-shifting the DMRS
pattern(s) described above. Specifically, the DMRS pattern may be
v-shifted according to the value of v-shift of the CRS (or
according to cell ID or cell ID mod 3).
[0335] In FIG. 11, an example of DMRS pattern with single antenna
port is shown where sPDCCH OFDM region consists of single OFDM
symbol. In this example, there are two DMRS REs per PRB with 6 REs
interval along a frequency axis. If multiple sPDCCHs are not
multiplexed within a PRB, DMRS transmission only for single antenna
port is enough and it can minimize DMRS overhead.
[0336] On the other hand, if multiplexing of multiple sPDCCHs
within a PRB is allowed or sPDCCH is transmitted using two antenna
ports (such as distributed ePDCCH transmission), DMRS pattern with
two antenna ports needs to be designed. DMRS pattern examples for
two antenna ports are shown in FIG. 36. As shown in FIG. 36(a),
DMRS REs for two antenna ports can be multiplexed by frequency
division multiplexing (FDM). Or, DMRS of two antenna ports can be
multiplexed within two adjacent DMRS REs by code division
multiplexing (CDM) as shown in FIG. 36(b) to maximize the number of
DMRS REs for each antenna port.
[0337] When sPDCCH region consists of two OFDM symbols, DMRS also
can be allocated in both OFDM symbols. For example, DMRS pattern
for single sPDCCH OFDM symbol can be copied in the second OFDM
symbol, or optimized DMRS patterns can be designed separately for
two sPDCCH OFDM symbols. On the other hand, even if the number of
sPDCCH OFDM symbols is two, DMRS can be allocated in the first OFDM
symbol only. It can help to reduce channel estimation latency. When
an sPDCCH OFDM symbol consists of 2 OFDM symbols, for example, DMRS
pattern(s) shown in FIG. 37 may be used.
[0338] FIGS. 37(a), 37(b), 37(c) and 37(d) illustrate exemplary
cases where one DMRS antenna port is provided. Referring to FIG.
37(a), a DMRS pattern used on a single sPDCCH OFDM symbol may
repeatedly appear on the first sPDCCH OFDM symbol and the second
sPDCCH OFDM symbol. Alternatively, as shown in FIG. 37(c) or 37(d),
a DMRS pattern separate from the DMRS pattern used on the single
sPDCCH OFDM symbol may be defined in case that the sPDCCH is
transmitted over 2 OFDM symbols. Alternatively, as shown in FIG.
37(b), even if the number of sPDCCH OFDM symbols is 2, the DMRS may
be present only on the first OFDM symbol. Alternatively, the DMRS
pattern used on the single sPDCCH OFDM symbol may appear only on an
OFDM symbol on which the sPDCCH is transmitted within a PRB. For
example, if the sPDCCH is transmitted only on the second OFDM
symbol, the DMRS pattern of FIG. 11 may be present only on the
second OFDM symbol. If the sPDCCH is transmitted over 2 OFDM
symbols, the DMRS pattern of FIG. 11 may be present on both OFDM
symbols as shown in FIG. 37(a).
[0339] If 2 DMRS antenna ports are provided, a DMRS pattern used on
a single sPDCCH OFDM symbol may repeatedly appear on the first
sPDCCH OFDM symbol and the second sPDCCH OFDM symbol.
Alternatively, as shown in FIG. 37(e) or 37(f), a DMRS pattern
separate from the DMRS pattern used on the single sPDCCH OFDM
symbol may be defined. Alternatively, as shown in FIG. 37(g) or
37(h), even if the number of sPDCCH OFDM symbols is 2, the DMRS may
be present only on the first OFDM symbol. Alternatively, the DMRS
pattern used on the single sPDCCH OFDM symbol may appear only on an
OFDM symbol on which the sPDCCH is transmitted within a PRB. For
example, if the sPDCCH is transmitted only on the second OFDM
symbol, the DMRS pattern of FIG. 36 may be present only on the
second OFDM symbol. If the sPDCCH is transmitted over 2 OFDM
symbols, the DMRS pattern of FIG. 36 may be present on both OFDM
symbols.
[0340] The DMRS patterns according to an embodiment of the present
invention include DMRS pattern(s) obtained by v-shifting the DMRS
pattern(s) described above. Specifically, the DMRS pattern may be
v-shifted according to the value of v-shift of the CRS (or
according to cell ID or cell ID mod 3).
[0341] G. DMRS Sharing Between sPDCCH and sPDSCH
[0342] If time division multiplexing (TDM) between sPDCCH and
sPDSCH is considered, for example, if placing sPDCCH in the first
one or two OFDM symbols of each sTTI is considered, DMRS for sPDSCH
can be allocated within OFDM symbols only for sPDSCH transmission.
In other word, sPDSCH DMRS cannot be allocated in OFDM symbol(s)
which sPDCCH can be transmitted in. For example, DMRS can be
located in the first two OFDM symbols after sPDCCH OFDM symbol
region as illustrated in FIG. 38(a). Or, as shown in FIG. 38(b),
DMRS REs can be located in the first OFDM symbol right after sPDCCH
OFDM symbol region to make channel estimation latency reduced as
much as possible. To reduce DMRS overhead, code division
multiplexing (CDM) of DMRSs for multiple antenna ports can be
adopted.
[0343] Making DMRS shared between sPDSCH and sPDCCH also can be
considered to reduce DMRS overhead. The RS for receiving the sPDCCH
and the sPDSCH is preferably located in the front part of the sTTI
or in the OFDM symbol (s) region in which the sPDCCH is transmitted
in order to reduce the latency for channel estimation and the
reception latency of the sPDCCH located in the front of the sTTI.
In order for the DMRS to be shared between the sPDCCH and the
sPDSCH, the RS for receiving the sPDCCH and receiving the sPDSCH is
located on the first OFDM symbol of the OFDM symbol region
constituting the sTTI. Or, to share DMRS among sPDCCH and sPDSCH,
DMRS antenna port(s) used for both sPDCCH and sPDSCH is allocated
within sPDCCH OFDM symbol(s). For example, let's assume that
antenna ports n and n+1 are used for sPDCCH and antenna ports n,
n+1, n+2, and n+3 are used for sPDSCH. Then, as illustrated in FIG.
38(c), DMRS for antenna ports n and n+1 which are shared by sPDCCH
and sPDSCH can be located in OFDM symbol(s) with sPDCCH
(hereinfater, sPDCCH OFDM symbol(s)), and DMRS for antenna ports
only for sPDSCH can be located after the sPDCCH OFDM symbol(s).
DMRS sharing can reduce DMRS overhead, but many issues should be
studied further such as DMRS OFDM symbol location, antenna port(s)
allocation, impacts on sPDCCH/sPDSCH performance, etc.
[0344] FIG. 39 is a block diagram illustrating elements of a
transmitting device 10 and a receiving device 20 for implementing
the present invention.
[0345] The transmitting device 10 and the receiving device 20
respectively include Radio Frequency (RF) units 13 and 23 capable
of transmitting and receiving radio signals carrying information,
data, signals, and/or messages, memories 12 and 22 for storing
information related to communication in a wireless communication
system, and processors 11 and 21 operationally connected to
elements such as the RF units 13 and 23 and the memories 12 and 22
to control the elements and configured to control the memories 12
and 22 and/or the RF units 13 and 23 so that a corresponding device
may perform at least one of the above-described embodiments of the
present invention.
[0346] The memories 12 and 22 may store programs for processing and
controlling the processors 11 and 21 and may temporarily store
input/output information. The memories 12 and 22 may be used as
buffers.
[0347] The processors 11 and 21 generally control the overall
operation of various modules in the transmitting device and the
receiving device. Especially, the processors 11 and 21 may perform
various control functions to implement the present invention. The
processors 11 and 21 may be referred to as controllers,
microcontrollers, microprocessors, or microcomputers. The
processors 11 and 21 may be implemented by hardware, firmware,
software, or a combination thereof. In a hardware configuration,
application specific integrated circuits (ASICs), digital signal
processors (DSPs), digital signal processing devices (DSPDs),
programmable logic devices (PLDs), or field programmable gate
arrays (FPGAs) may be included in the processors 11 and 21.
Meanwhile, if the present invention is implemented using firmware
or software, the firmware or software may be configured to include
modules, procedures, functions, etc. performing the functions or
operations of the present invention. Firmware or software
configured to perform the present invention may be included in the
processors 11 and 21 or stored in the memories 12 and 22 so as to
be driven by the processors 11 and 21.
[0348] The processor 11 of the transmitting device 10 performs
predetermined coding and modulation for a signal and/or data
scheduled to be transmitted to the outside by the processor 11 or a
scheduler connected with the processor 11, and then transfers the
coded and modulated data to the RF unit 13. For example, the
processor 11 converts a data stream to be transmitted into K layers
through demultiplexing, channel coding, scrambling, and modulation.
The coded data stream is also referred to as a codeword and is
equivalent to a transport block which is a data block provided by a
MAC layer. One transport block (TB) is coded into one codeword and
each codeword is transmitted to the receiving device in the form of
one or more layers. For frequency up-conversion, the RF unit 13 may
include an oscillator. The RF unit 13 may include Nt (where Nt is a
positive integer) transmit antennas.
[0349] A signal processing process of the receiving device 20 is
the reverse of the signal processing process of the transmitting
device 10. Under control of the processor 21, the RF unit 23 of the
receiving device 20 receives radio signals transmitted by the
transmitting device 10. The RF unit 23 may include N.sub.r (where
N.sub.r is a positive integer) receive antennas and frequency
down-converts each signal received through receive antennas into a
baseband signal. The processor 21 decodes and demodulates the radio
signals received through the receive antennas and restores data
that the transmitting device 10 intended to transmit.
[0350] The RF units 13 and 23 include one or more antennas. An
antenna performs a function for transmitting signals processed by
the RF units 13 and 23 to the exterior or receiving radio signals
from the exterior to transfer the radio signals to the RF units 13
and 23. The antenna may also be called an antenna port. Each
antenna may correspond to one physical antenna or may be configured
by a combination of more than one physical antenna element. The
signal transmitted from each antenna cannot be further
deconstructed by the receiving device 20. An RS transmitted through
a corresponding antenna defines an antenna from the view point of
the receiving device 20 and enables the receiving device 20 to
derive channel estimation for the antenna, irrespective of whether
the channel represents a single radio channel from one physical
antenna or a composite channel from a plurality of physical antenna
elements including the antenna. That is, an antenna is defined such
that a channel carrying a symbol of the antenna can be obtained
from a channel carrying another symbol of the same antenna. An RF
unit supporting a MIMO function of transmitting and receiving data
using a plurality of antennas may be connected to two or more
antennas.
[0351] In the embodiments of the present invention, a UE operates
as the transmitting device 10 in UL and as the receiving device 20
in DL. In the embodiments of the present invention, an eNB operates
as the receiving device 20 in UL and as the transmitting device 10
in DL. Hereinafter, a processor, an RF unit, and a memory included
in the UE will be referred to as a UE processor, a UE RF unit, and
a UE memory, respectively, and a processor, an RF unit, and a
memory included in the eNB will be referred to as an eNB processor,
an eNB RF unit, and an eNB memory, respectively.
[0352] The eNB processor may configure sTTIs in the entire channel
band or on some frequency resources. The eNB processor may
configure one or more sTTIs in a default TTI. The eNB processor may
control the eNB RF to transmit information indicating the frequency
resources having configured sTTIs and/or information indicating
time resources having configured sTTIs.
[0353] The eNB processor may control the eNB RF unit to transmit an
sPDCCH and/or sPDSCH (hereinafter, sPDCCH/sPDSCH) within an sTTI
according to one of the suggestions of the present invention
disclosed above. The eNB processor may control the eNB RF unit to
transmit an RS for demodulation of the sPDCCH/sPDSCH (hereinafter,
DMRS) in the sTTI. The eNB processor may control the eNB RF unit to
transmit, within an OFDM symbol having the sPDCCH, DMRS(s) for
antenna port(s) used for transmission of both the sPDCCH and the
sPDSCH. The eNB processor may control the eNB RF unit to transmit,
within the remaining OFDM symbol(s) without the sPDCCH, DMRS(s) for
antenna port(s) used only for transmission of the sPDSCH.
[0354] The eNB processor may apply a DMRS based TM to the
sPDCCH/sPDSCH if the sTTI has only OFDM symbols without the CRS.
The eNB processor may apply a CRS based TM to an sTTI including
OFDM symbols with the CRS. The eNB processor may control the eNB RF
unit to transmit an sPDCCH/sPDSCH along with the CRS but without
the DMRS within the sTTI having the CRS. When the processor
transmits a control/data channel to a UE assigned configuration of
a DMRS-based TM, it may control the eNB RF unit to transmit the
control/data channel based on the DMRS within a TTI/sTTI without
the CRS and to transmit the control/data channel based on the CRS
rather than on the DMRS within a TTI/sTTI with the CRS.
Alternatively, the eNB processor may configure a TM for the
TTI/sTTI without the CRS and a TM for the TTI/sTTI with the CRS
separately. The eNB processor may configure one of the DMRS based
TMs as the TM for the TTI/sTTI without the CRS and one of the CRS
based TMs as the TM for the TTI/sTTI with the CRS. The eNB
processor may control the eNB RF unit to transmit information about
the TM for the TTI/sTTI without the CRS and information about the
TM for the TTI/sTTI with the CRS to the UE.
[0355] The UE processor may control the UE RF to receive frequency
resource information indicating the frequency resources having
configured sTTIs and/or time resource information indicating time
resources having configured sTTIs. The UE processor may configure
sTTIs in the entire channel band or on some frequency resources,
based on the frequency resource information. The UE processor may
configure one or more sTTIs in a default TTI based on the time
resource information.
[0356] The UE processor may control the UE RF unit to receive an
sPDCCH and/or sPDSCH (hereinafter, sPDCCH/sPDSCH) within an sTTI
according to one of the suggestions of the present invention
disclosed above. The UE processor may control the UE RF unit to
receive an RS for demodulation of the sPDCCH/sPDSCH (hereinafter,
DMRS) in the sTTI. The UE processor may control the UE RF unit to
receive, within an OFDM symbol having the sPDCCH, DMRS(s) for
antenna port(s) used for transmission of both the sPDCCH and the
sPDSCH. The UE processor may control the UE RF unit to receive,
within the remaining OFDM symbol(s) without the sPDCCH, DMRS(s) for
antenna port(s) used only for transmission of the sPDSCH.
[0357] If the sTTI has only OFDM symbols without the CRS, the UE
processor may assume that the sPDCCH/sPDSCH is transmitted within
the sTTI based on the DMRS. Thereby, if the sTTI has only OFDM
symbols without the CRS, the UE processor may demodulate or decode
the received sPDCCH/sPDSCH within the sTTI, based on the DMRS. In
an sTTI having OFDM symbols with the CRS, the UE processor may
assume that the sPDCCH/sPDSCH is transmitted based on the CRS. The
UE processor may not expect reception of a DMRS in an sTTI with the
CRS, and may demodulate or decode an sPDCCH/sPDSCH received in the
sTTI with the CRS, based on the CRS. If the value is set in a DMRS
based TM, the UE processor may demodulate or decode the
control/data channel based on the DMRS within a TTI/sTTI without
the CRS, and may demodulate or decode the control/data channel
based on the CRS rather than on the DMRS within a TTI/sTTI with the
CRS. Alternatively, the UE processor may control the UE RFE unit to
receive transmission mode information having a TM for the TTI/sTTI
without the CRS and a TM for the TTI/sTTI with the CRS which are
configured separately. The UE processor may
receive/demodulate/decode the sPDCCH/sPDSCH according to a DMRS
based TM configured for the UE among the DMRS based TMs in the
TTI/sTTI without the CRS, and may receive/demodulate/decode the
sPDCCH/sPDSCH according to a CRS based TM configured for the UE in
the TTI/sTTI with the CRS.
[0358] As described above, the detailed description of the
preferred embodiments of the present invention has been given to
enable those skilled in the art to implement and practice the
invention. Although the invention has been described with reference
to exemplary embodiments, those skilled in the art will appreciate
that various modifications and variations can be made in the
present invention without departing from the spirit or scope of the
invention described in the appended claims. Accordingly, the
invention should not be limited to the specific embodiments
described herein, but should be accorded the broadest scope
consistent with the principles and novel features disclosed
herein.
* * * * *
References